From f31d9a3e76b21bb3644f3775fb80e846383e2890 Mon Sep 17 00:00:00 2001
From: Tanmay Deep Sharma <tanmaydeepsharma21@gmail.com>
Date: Wed, 29 Oct 2025 20:29:09 +0530
Subject: [PATCH 1/3] store next billing dates

---
 .../api/v1/models/_account.json.jbuilder      |  4 ++++
 .../billing/v2/change_plan_service.rb         | 18 +++++++++++++-
 .../v2/subscription_provisioning_service.rb   |  4 +++-
 .../billing/v2/update_subscription_service.rb | 24 +++++++++++++------
 4 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/app/views/api/v1/models/_account.json.jbuilder b/app/views/api/v1/models/_account.json.jbuilder
index af9235b4b..ba74e5c94 100644
--- a/app/views/api/v1/models/_account.json.jbuilder
+++ b/app/views/api/v1/models/_account.json.jbuilder
@@ -6,6 +6,10 @@ if resource.custom_attributes.present?
     json.subscribed_quantity resource.custom_attributes['subscribed_quantity']
     json.subscription_status resource.custom_attributes['subscription_status']
     json.subscription_ends_on resource.custom_attributes['subscription_ends_on']
+    json.stripe_subscription_id resource.custom_attributes['stripe_subscription_id'] if resource.custom_attributes['stripe_subscription_id'].present?
+    json.pending_stripe_pricing_plan_id resource.custom_attributes['pending_stripe_pricing_plan_id'] if resource.custom_attributes['pending_stripe_pricing_plan_id'].present?
+    json.pending_subscription_quantity resource.custom_attributes['pending_subscription_quantity'] if resource.custom_attributes['pending_subscription_quantity'].present?
+    json.next_billing_date resource.custom_attributes['next_billing_date'] if resource.custom_attributes['next_billing_date'].present?
     json.industry resource.custom_attributes['industry'] if resource.custom_attributes['industry'].present?
     json.company_size resource.custom_attributes['company_size'] if resource.custom_attributes['company_size'].present?
     json.timezone resource.custom_attributes['timezone'] if resource.custom_attributes['timezone'].present?
diff --git a/enterprise/app/services/enterprise/billing/v2/change_plan_service.rb b/enterprise/app/services/enterprise/billing/v2/change_plan_service.rb
index e300b83e7..8e3ff74fe 100644
--- a/enterprise/app/services/enterprise/billing/v2/change_plan_service.rb
+++ b/enterprise/app/services/enterprise/billing/v2/change_plan_service.rb
@@ -27,6 +27,7 @@ class Enterprise::Billing::V2::ChangePlanService < Enterprise::Billing::V2::Base
   def create_change_plan_intent(new_pricing_plan_id, quantity)
     subscription_id = fetch_subscription_id
     cadence_id = fetch_cadence_from_subscription(subscription_id)
+    store_next_billing_date(cadence_id)
     plan_version = fetch_new_plan_version(new_pricing_plan_id)
     lookup_key = fetch_plan_lookup_key(new_pricing_plan_id)
     component_config = { lookup_key: lookup_key, quantity: quantity }
@@ -120,10 +121,25 @@ class Enterprise::Billing::V2::ChangePlanService < Enterprise::Billing::V2::Base
     )
   end
 
+  def retrieve_billing_cadence(cadence_id)
+    StripeV2Client.request(
+      :get,
+      "/v2/billing/cadences/#{cadence_id}",
+      {},
+      stripe_api_options
+    )
+  end
+
+  def store_next_billing_date(cadence_id)
+    cadence = retrieve_billing_cadence(cadence_id)
+    @next_billing_date = extract_attribute(cadence, :next_billing_date)
+  end
+
   def update_account_plan(new_pricing_plan_id, quantity)
     attributes = {
       'pending_stripe_pricing_plan_id' => new_pricing_plan_id,
-      'pending_subscription_quantity' => quantity
+      'pending_subscription_quantity' => quantity,
+      'next_billing_date' => @next_billing_date
     }
 
     # Add plan name from catalog
diff --git a/enterprise/app/services/enterprise/billing/v2/subscription_provisioning_service.rb b/enterprise/app/services/enterprise/billing/v2/subscription_provisioning_service.rb
index 741ad3b99..66c76262d 100644
--- a/enterprise/app/services/enterprise/billing/v2/subscription_provisioning_service.rb
+++ b/enterprise/app/services/enterprise/billing/v2/subscription_provisioning_service.rb
@@ -120,7 +120,9 @@ class Enterprise::Billing::V2::SubscriptionProvisioningService < Enterprise::Bil
       'subscription_status' => 'active',
       'pending_subscription_quantity' => nil,
       'pending_subscription_pricing_plan' => nil,
-      'billing_cadence' => billing_cadence
+      'billing_cadence' => billing_cadence,
+      'next_billing_date' => nil,
+      'pending_stripe_pricing_plan_id' => nil
     }
     attributes['stripe_pricing_plan_id'] = pricing_plan_id if pricing_plan_id.present?
 
diff --git a/enterprise/app/services/enterprise/billing/v2/update_subscription_service.rb b/enterprise/app/services/enterprise/billing/v2/update_subscription_service.rb
index a4f10b127..0f6328fe5 100644
--- a/enterprise/app/services/enterprise/billing/v2/update_subscription_service.rb
+++ b/enterprise/app/services/enterprise/billing/v2/update_subscription_service.rb
@@ -29,11 +29,11 @@ class Enterprise::Billing::V2::UpdateSubscriptionService < Enterprise::Billing::
     subscription_id = fetch_subscription_id
     subscription = retrieve_pricing_plan_subscription(subscription_id)
     cadence_id, plan_id, plan_version = extract_subscription_details(subscription)
+    store_next_billing_date(cadence_id)
     lookup_key = fetch_plan_lookup_key(plan_id)
     component_config = { lookup_key: lookup_key, quantity: quantity }
 
     params = build_modify_params(subscription_id, cadence_id, plan_id, plan_version, component_config)
-    log_modify_intent(params)
 
     StripeV2Client.request(:post, '/v2/billing/intents', params, stripe_api_options)
   end
@@ -81,11 +81,6 @@ class Enterprise::Billing::V2::UpdateSubscriptionService < Enterprise::Billing::
     }
   end
 
-  def log_modify_intent(params)
-    Rails.logger.info "Create modify intent params: #{params.inspect}"
-    Rails.logger.info "Stripe API options: #{stripe_api_options.inspect}"
-  end
-
   def reserve_billing_intent(billing_intent)
     StripeV2Client.request(
       :post,
@@ -113,9 +108,24 @@ class Enterprise::Billing::V2::UpdateSubscriptionService < Enterprise::Billing::
     )
   end
 
+  def retrieve_billing_cadence(cadence_id)
+    StripeV2Client.request(
+      :get,
+      "/v2/billing/cadences/#{cadence_id}",
+      {},
+      stripe_api_options
+    )
+  end
+
+  def store_next_billing_date(cadence_id)
+    cadence = retrieve_billing_cadence(cadence_id)
+    @next_billing_date = extract_attribute(cadence, :next_billing_date)
+  end
+
   def update_account_quantity(quantity)
     update_custom_attributes({
-                               'pending_subscription_quantity' => quantity
+                               'pending_subscription_quantity' => quantity,
+                               'next_billing_date' => @next_billing_date
                              })
   end
 

From 94985bbc77c1abfc861b8d6a1d8ce0f5e1ed1947 Mon Sep 17 00:00:00 2001
From: Tanmay Deep Sharma <tanmaydeepsharma21@gmail.com>
Date: Wed, 29 Oct 2025 21:35:08 +0530
Subject: [PATCH 2/3] remove update subscription flow overall

---
 app/policies/account_policy.rb                |   4 -
 config/routes.rb                              |   1 -
 .../api/v1/accounts/concerns/billing_v2.rb    |  16 --
 .../billing/v2/update_subscription_service.rb | 147 ------------------
 4 files changed, 168 deletions(-)
 delete mode 100644 enterprise/app/services/enterprise/billing/v2/update_subscription_service.rb

diff --git a/app/policies/account_policy.rb b/app/policies/account_policy.rb
index ee5e2b37f..212af6c34 100644
--- a/app/policies/account_policy.rb
+++ b/app/policies/account_policy.rb
@@ -59,10 +59,6 @@ class AccountPolicy < ApplicationPolicy
     @account_user.administrator?
   end
 
-  def update_subscription_quantity?
-    @account_user.administrator?
-  end
-
   def change_pricing_plan?
     @account_user.administrator?
   end
diff --git a/config/routes.rb b/config/routes.rb
index b8dc61d1b..28826d84c 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -439,7 +439,6 @@ Rails.application.routes.draw do
               post :v2_topup
               post :v2_subscribe
               post :cancel_subscription
-              post :update_subscription_quantity
               post :change_pricing_plan
             end
           end
diff --git a/enterprise/app/controllers/enterprise/api/v1/accounts/concerns/billing_v2.rb b/enterprise/app/controllers/enterprise/api/v1/accounts/concerns/billing_v2.rb
index 6fa71998a..97c6c22cc 100644
--- a/enterprise/app/controllers/enterprise/api/v1/accounts/concerns/billing_v2.rb
+++ b/enterprise/app/controllers/enterprise/api/v1/accounts/concerns/billing_v2.rb
@@ -77,22 +77,6 @@ module Enterprise::Api::V1::Accounts::Concerns::BillingV2
     end
   end
 
-  def update_subscription_quantity
-    service = Enterprise::Billing::V2::UpdateSubscriptionService.new(account: @account)
-    result = service.update_quantity(quantity: params[:quantity].to_i)
-
-    if result[:success]
-      # Include account ID and updated attributes for frontend store update
-      @account.reload
-      render json: result.merge(
-        id: @account.id,
-        custom_attributes: @account.custom_attributes
-      )
-    else
-      render json: { error: result[:message] }, status: :unprocessable_entity
-    end
-  end
-
   def change_pricing_plan
     service = Enterprise::Billing::V2::ChangePlanService.new(account: @account)
     result = service.change_plan(
diff --git a/enterprise/app/services/enterprise/billing/v2/update_subscription_service.rb b/enterprise/app/services/enterprise/billing/v2/update_subscription_service.rb
deleted file mode 100644
index 0f6328fe5..000000000
--- a/enterprise/app/services/enterprise/billing/v2/update_subscription_service.rb
+++ /dev/null
@@ -1,147 +0,0 @@
-class Enterprise::Billing::V2::UpdateSubscriptionService < Enterprise::Billing::V2::BaseService
-  include Enterprise::Billing::Concerns::PlanFeatureManager
-
-  # Update subscription quantity using Stripe's V2 Billing Intent API
-  # Creates a modify billing intent to change the subscription quantity
-  #
-  # @param quantity [Integer] The new quantity
-  # @return [Hash] { success:, message: }
-  #
-  def update_quantity(quantity:)
-    return { success: false, message: 'Invalid quantity' } unless quantity.positive?
-
-    with_locked_account do
-      billing_intent = create_modify_intent(quantity)
-      reserve_billing_intent(billing_intent)
-      commit_billing_intent(billing_intent)
-      update_account_quantity(quantity)
-      success_response(quantity)
-    end
-  rescue Stripe::StripeError => e
-    { success: false, message: "Stripe error: #{e.message}" }
-  rescue StandardError => e
-    { success: false, message: "Update error: #{e.message}" }
-  end
-
-  private
-
-  def create_modify_intent(quantity)
-    subscription_id = fetch_subscription_id
-    subscription = retrieve_pricing_plan_subscription(subscription_id)
-    cadence_id, plan_id, plan_version = extract_subscription_details(subscription)
-    store_next_billing_date(cadence_id)
-    lookup_key = fetch_plan_lookup_key(plan_id)
-    component_config = { lookup_key: lookup_key, quantity: quantity }
-
-    params = build_modify_params(subscription_id, cadence_id, plan_id, plan_version, component_config)
-
-    StripeV2Client.request(:post, '/v2/billing/intents', params, stripe_api_options)
-  end
-
-  def fetch_subscription_id
-    custom_attribute('stripe_subscription_id').tap do |id|
-      raise StandardError, 'No pricing plan subscription ID found' if id.blank?
-    end
-  end
-
-  def extract_subscription_details(subscription)
-    cadence = extract_attribute(subscription, :billing_cadence)
-    plan = extract_attribute(subscription, :pricing_plan)
-    version = extract_attribute(subscription, :pricing_plan_version)
-
-    raise StandardError, 'No billing cadence found in subscription' if cadence.blank?
-    raise StandardError, 'No pricing plan found in subscription' if plan.blank?
-    raise StandardError, 'No pricing plan version found in subscription' if version.blank?
-
-    [cadence, plan, version]
-  end
-
-  def fetch_plan_lookup_key(plan_id)
-    Enterprise::Billing::V2::PlanCatalog.lookup_key_for_plan(plan_id).tap do |key|
-      raise StandardError, "Lookup key not found for pricing plan #{plan_id}" unless key
-    end
-  end
-
-  def build_modify_params(subscription_id, cadence_id, plan_id, plan_version, component_config)
-    {
-      cadence: cadence_id,
-      currency: 'usd',
-      actions: [{
-        type: 'modify',
-        modify: {
-          type: 'pricing_plan_subscription_details',
-          pricing_plan_subscription_details: {
-            pricing_plan_subscription: subscription_id,
-            new_pricing_plan: plan_id,
-            new_pricing_plan_version: plan_version,
-            component_configurations: [component_config]
-          }
-        }
-      }]
-    }
-  end
-
-  def reserve_billing_intent(billing_intent)
-    StripeV2Client.request(
-      :post,
-      "/v2/billing/intents/#{billing_intent.id}/reserve",
-      {},
-      stripe_api_options
-    )
-  end
-
-  def commit_billing_intent(billing_intent)
-    StripeV2Client.request(
-      :post,
-      "/v2/billing/intents/#{billing_intent.id}/commit",
-      {},
-      stripe_api_options
-    )
-  end
-
-  def retrieve_pricing_plan_subscription(subscription_id)
-    StripeV2Client.request(
-      :get,
-      "/v2/billing/pricing_plan_subscriptions/#{subscription_id}",
-      {},
-      stripe_api_options
-    )
-  end
-
-  def retrieve_billing_cadence(cadence_id)
-    StripeV2Client.request(
-      :get,
-      "/v2/billing/cadences/#{cadence_id}",
-      {},
-      stripe_api_options
-    )
-  end
-
-  def store_next_billing_date(cadence_id)
-    cadence = retrieve_billing_cadence(cadence_id)
-    @next_billing_date = extract_attribute(cadence, :next_billing_date)
-  end
-
-  def update_account_quantity(quantity)
-    update_custom_attributes({
-                               'pending_subscription_quantity' => quantity,
-                               'next_billing_date' => @next_billing_date
-                             })
-  end
-
-  def success_response(quantity)
-    {
-      success: true,
-      quantity: quantity,
-      message: "Subscription quantity updated to #{quantity}"
-    }
-  end
-
-  def stripe_api_options
-    { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-  end
-
-  def extract_attribute(object, key)
-    object.respond_to?(key) ? object.public_send(key) : object[key.to_s]
-  end
-end

From ce5a859a4fad2cbf688cea3e5dfcdd327908e9c0 Mon Sep 17 00:00:00 2001
From: Tanmay Deep Sharma <tanmaydeepsharma21@gmail.com>
Date: Thu, 30 Oct 2025 15:51:51 +0530
Subject: [PATCH 3/3] create and pay an invoice on subscription change

---
 .../concerns/plan_provisioning_helper.rb      |  44 +++
 .../concerns/proration_line_item_builder.rb   | 103 ++++++++
 .../concerns/stripe_v2_client_helper.rb       | 120 +++++++++
 .../billing/handle_stripe_event_service.rb    |   5 +-
 .../billing/v2/cancel_subscription_service.rb |  52 +---
 .../billing/v2/change_plan_service.rb         | 250 ++++++++++--------
 .../billing/v2/checkout_session_service.rb    |  17 +-
 .../billing/v2/invoice_payment_service.rb     | 111 ++++++++
 .../v2/pricing_plan_component_builder.rb      |  91 ++-----
 .../billing/v2/pricing_plan_service.rb        |  30 +--
 .../billing/v2/proration_calculator.rb        |  99 +++++++
 .../v2/subscription_provisioning_service.rb   |  14 +-
 .../enterprise/billing/v2/topup_service.rb    | 114 +++-----
 .../billing/v2/webhook_handler_service.rb     |  20 +-
 14 files changed, 701 insertions(+), 369 deletions(-)
 create mode 100644 enterprise/app/services/enterprise/billing/concerns/plan_provisioning_helper.rb
 create mode 100644 enterprise/app/services/enterprise/billing/concerns/proration_line_item_builder.rb
 create mode 100644 enterprise/app/services/enterprise/billing/concerns/stripe_v2_client_helper.rb
 create mode 100644 enterprise/app/services/enterprise/billing/v2/invoice_payment_service.rb
 create mode 100644 enterprise/app/services/enterprise/billing/v2/proration_calculator.rb

diff --git a/enterprise/app/services/enterprise/billing/concerns/plan_provisioning_helper.rb b/enterprise/app/services/enterprise/billing/concerns/plan_provisioning_helper.rb
new file mode 100644
index 000000000..4f53a899c
--- /dev/null
+++ b/enterprise/app/services/enterprise/billing/concerns/plan_provisioning_helper.rb
@@ -0,0 +1,44 @@
+module Enterprise::Billing::Concerns::PlanProvisioningHelper
+  extend ActiveSupport::Concern
+
+  private
+
+  def provision_new_plan(new_pricing_plan_id)
+    sync_plan_credits(new_pricing_plan_id)
+
+    plan_definition = Enterprise::Billing::V2::PlanCatalog.definition_for(new_pricing_plan_id)
+    if plan_definition
+      plan_name = extract_plan_name(plan_definition)
+      enable_plan_specific_features(plan_name) if plan_name.present?
+    end
+
+    reset_captain_usage
+  end
+
+  def sync_plan_credits(pricing_plan_id)
+    plan_credits = Enterprise::Billing::V2::PlanCatalog.monthly_credits_for(pricing_plan_id)
+
+    Enterprise::Billing::V2::CreditManagementService
+      .new(account: account)
+      .sync_monthly_credits(plan_credits.to_i)
+  end
+
+  def extract_plan_name(plan_definition)
+    plan_definition[:display_name].split.find { |word| %w[Startup Startups Business Enterprise].include?(word) }
+  end
+
+  def update_account_plan(new_pricing_plan_id, quantity, next_billing_date)
+    attributes = {
+      'stripe_pricing_plan_id' => new_pricing_plan_id,
+      'pending_stripe_pricing_plan_id' => nil,
+      'pending_subscription_quantity' => nil,
+      'subscribed_quantity' => quantity,
+      'next_billing_date' => next_billing_date
+    }
+
+    plan_definition = Enterprise::Billing::V2::PlanCatalog.definition_for(new_pricing_plan_id)
+    attributes['plan_name'] = plan_definition[:display_name] if plan_definition
+
+    update_custom_attributes(attributes)
+  end
+end
diff --git a/enterprise/app/services/enterprise/billing/concerns/proration_line_item_builder.rb b/enterprise/app/services/enterprise/billing/concerns/proration_line_item_builder.rb
new file mode 100644
index 000000000..fa04dfeb8
--- /dev/null
+++ b/enterprise/app/services/enterprise/billing/concerns/proration_line_item_builder.rb
@@ -0,0 +1,103 @@
+module Enterprise::Billing::Concerns::ProrationLineItemBuilder
+  extend ActiveSupport::Concern
+
+  private
+
+  def build_proration_line_items(context, proration_data)
+    return build_seat_change_line_items(context, proration_data) if seat_only_change?(context)
+
+    build_plan_change_line_items(context, proration_data)
+  end
+
+  def seat_only_change?(context)
+    !context[:plan_changed] && context[:seats_changed]
+  end
+
+  def build_seat_change_line_items(context, proration_data)
+    [{
+      amount: (proration_data[:net_amount] * 100).to_i,
+      description: build_seat_change_description(context),
+      metadata: build_seat_change_metadata(context, proration_data)
+    }]
+  end
+
+  def build_plan_change_line_items(context, proration_data)
+    line_items = []
+    old_plan_name = plan_display_name(context[:old_plan_id])
+    new_plan_name = plan_display_name(context[:target_plan_id])
+
+    line_items << build_credit_line_item(context, proration_data, old_plan_name) if proration_data[:credit_amount].positive?
+    line_items << build_charge_line_item(context, proration_data, new_plan_name) if proration_data[:charge_amount].positive?
+
+    line_items
+  end
+
+  def plan_display_name(plan_id)
+    Enterprise::Billing::V2::PlanCatalog.definition_for(plan_id)&.dig(:display_name) || 'Unknown Plan'
+  end
+
+  def build_credit_line_item(context, proration_data, old_plan_name)
+    {
+      amount: -(proration_data[:credit_amount] * 100).to_i,
+      description: credit_description(old_plan_name, context[:old_quantity]),
+      metadata: credit_metadata(old_plan_name, context[:old_quantity], proration_data[:days_remaining])
+    }
+  end
+
+  def build_charge_line_item(context, proration_data, new_plan_name)
+    {
+      amount: (proration_data[:charge_amount] * 100).to_i,
+      description: charge_description(new_plan_name, context[:target_quantity]),
+      metadata: charge_metadata(new_plan_name, context[:target_quantity], proration_data[:days_remaining])
+    }
+  end
+
+  def credit_description(plan_name, quantity)
+    "Credit for unused time on #{plan_name} (#{quantity} seat#{quantity > 1 ? 's' : ''})"
+  end
+
+  def charge_description(plan_name, quantity)
+    "Prorated charge for #{plan_name} (#{quantity} seat#{quantity > 1 ? 's' : ''})"
+  end
+
+  def credit_metadata(plan_name, quantity, days_remaining)
+    {
+      type: 'proration_credit',
+      old_plan: plan_name,
+      old_quantity: quantity,
+      days_remaining: days_remaining,
+      billing_version: 'v2'
+    }
+  end
+
+  def charge_metadata(plan_name, quantity, days_remaining)
+    {
+      type: 'proration_charge',
+      new_plan: plan_name,
+      new_quantity: quantity,
+      days_remaining: days_remaining,
+      billing_version: 'v2'
+    }
+  end
+
+  def build_seat_change_description(context)
+    plan_name = plan_display_name(context[:target_plan_id])
+    change_type = context[:target_quantity] > context[:old_quantity] ? 'increase' : 'decrease'
+    quantity_diff = (context[:target_quantity] - context[:old_quantity]).abs
+
+    "Seat #{change_type} for #{plan_name}: #{context[:old_quantity]} → #{context[:target_quantity]} " \
+      "seats (#{quantity_diff} seat#{quantity_diff > 1 ? 's' : ''})"
+  end
+
+  def build_seat_change_metadata(context, proration_data)
+    {
+      type: 'seat_change',
+      plan_name: plan_display_name(context[:target_plan_id]),
+      old_quantity: context[:old_quantity],
+      new_quantity: context[:target_quantity],
+      quantity_change: context[:target_quantity] - context[:old_quantity],
+      days_remaining: proration_data[:days_remaining],
+      billing_version: 'v2'
+    }
+  end
+end
diff --git a/enterprise/app/services/enterprise/billing/concerns/stripe_v2_client_helper.rb b/enterprise/app/services/enterprise/billing/concerns/stripe_v2_client_helper.rb
new file mode 100644
index 000000000..e7f2e39d9
--- /dev/null
+++ b/enterprise/app/services/enterprise/billing/concerns/stripe_v2_client_helper.rb
@@ -0,0 +1,120 @@
+module Enterprise::Billing::Concerns::StripeV2ClientHelper
+  extend ActiveSupport::Concern
+
+  private
+
+  # Generic Stripe V2 API request wrapper
+  def stripe_v2_request(method, path, params = {}, api_version: nil)
+    StripeV2Client.request(method, path, params, stripe_api_options(api_version))
+  end
+
+  # Pricing Plan Subscriptions
+  def retrieve_pricing_plan_subscription(subscription_id)
+    stripe_v2_request(:get, "/v2/billing/pricing_plan_subscriptions/#{subscription_id}")
+  end
+
+  # Pricing Plans
+  def retrieve_pricing_plan(pricing_plan_id)
+    stripe_v2_request(:get, "/v2/billing/pricing_plans/#{pricing_plan_id}")
+  end
+
+  def create_pricing_plan(params)
+    stripe_v2_request(:post, '/v2/billing/pricing_plans', params)
+  end
+
+  def update_pricing_plan(plan_id, params)
+    stripe_v2_request(:post, "/v2/billing/pricing_plans/#{plan_id}", params)
+  end
+
+  # Billing Cadences
+  def retrieve_billing_cadence(cadence_id)
+    stripe_v2_request(:get, "/v2/billing/cadences/#{cadence_id}")
+  end
+
+  # Billing Intents
+  def create_billing_intent(params)
+    stripe_v2_request(:post, '/v2/billing/intents', params)
+  end
+
+  def reserve_billing_intent(billing_intent)
+    stripe_v2_request(:post, "/v2/billing/intents/#{billing_intent.id}/reserve")
+  end
+
+  def commit_billing_intent(billing_intent)
+    stripe_v2_request(:post, "/v2/billing/intents/#{billing_intent.id}/commit")
+  end
+
+  # Custom Pricing Units
+  def create_custom_pricing_unit(params)
+    stripe_v2_request(:post, '/v2/billing/custom_pricing_units', params)
+  end
+
+  # Licensed Items
+  def create_licensed_item(params)
+    stripe_v2_request(:post, '/v2/billing/licensed_items', params)
+  end
+
+  # License Fees
+  def create_license_fee(params)
+    stripe_v2_request(:post, '/v2/billing/license_fees', params)
+  end
+
+  # Service Actions
+  def create_service_action(params)
+    stripe_v2_request(:post, '/v2/billing/service_actions', params)
+  end
+
+  # Rate Cards
+  def create_rate_card(params)
+    stripe_v2_request(:post, '/v2/billing/rate_cards', params)
+  end
+
+  def add_rate_to_card(card_id, params)
+    stripe_v2_request(:post, "/v2/billing/rate_cards/#{card_id}/rates", params)
+  end
+
+  # Metered Items
+  def create_metered_item(params)
+    stripe_v2_request(:post, '/v2/billing/metered_items', params)
+  end
+
+  # Meters (V1 API but used with V2)
+  def create_meter(params)
+    stripe_v2_request(:post, '/v1/billing/meters', params)
+  end
+
+  # Pricing Plan Components
+  def add_pricing_plan_component(plan_id, params)
+    stripe_v2_request(:post, "/v2/billing/pricing_plans/#{plan_id}/components", params)
+  end
+
+  # Checkout Sessions (V1 API but used with V2 plans)
+  def create_checkout_session(params, api_version: nil)
+    stripe_v2_request(:post, '/v1/checkout/sessions', params, api_version: api_version)
+  end
+
+  # Credit Grants (V1 API but used with V2)
+  def retrieve_credit_grant(grant_id)
+    stripe_v2_request(:get, "/v1/billing/credit_grants/#{grant_id}")
+  end
+
+  # API Options with support for custom versions
+  def stripe_api_options(custom_version = nil)
+    {
+      api_key: ENV.fetch('STRIPE_SECRET_KEY', nil),
+      stripe_version: custom_version || default_stripe_version
+    }
+  end
+
+  def default_stripe_version
+    '2025-08-27.preview'
+  end
+
+  def checkout_stripe_version
+    '2025-08-27.preview;checkout_product_catalog_preview=v1'
+  end
+
+  def extract_attribute(object, key)
+    object.respond_to?(key) ? object.public_send(key) : object[key.to_s]
+  end
+end
diff --git a/enterprise/app/services/enterprise/billing/handle_stripe_event_service.rb b/enterprise/app/services/enterprise/billing/handle_stripe_event_service.rb
index bb1df4f54..820b2a001 100644
--- a/enterprise/app/services/enterprise/billing/handle_stripe_event_service.rb
+++ b/enterprise/app/services/enterprise/billing/handle_stripe_event_service.rb
@@ -1,5 +1,6 @@
 class Enterprise::Billing::HandleStripeEventService
   include Enterprise::Billing::Concerns::PlanFeatureManager
+  include Enterprise::Billing::Concerns::StripeV2ClientHelper
 
   CLOUD_PLANS_CONFIG = 'CHATWOOT_CLOUD_PLANS'.freeze
 
@@ -124,10 +125,6 @@ class Enterprise::Billing::HandleStripeEventService
     grant_object.respond_to?(:id) ? grant_object.id : grant_object['id']
   end
 
-  def retrieve_credit_grant(grant_id)
-    StripeV2Client.request(:get, "/v1/billing/credit_grants/#{grant_id}")
-  end
-
   def extract_credit_amount(grant)
     # First, try to get credits from metadata
     metadata = extract_attribute(grant, :metadata)
diff --git a/enterprise/app/services/enterprise/billing/v2/cancel_subscription_service.rb b/enterprise/app/services/enterprise/billing/v2/cancel_subscription_service.rb
index 34fa145ae..9c4e163ae 100644
--- a/enterprise/app/services/enterprise/billing/v2/cancel_subscription_service.rb
+++ b/enterprise/app/services/enterprise/billing/v2/cancel_subscription_service.rb
@@ -1,5 +1,6 @@
 class Enterprise::Billing::V2::CancelSubscriptionService < Enterprise::Billing::V2::BaseService
   include Enterprise::Billing::Concerns::PlanFeatureManager
+  include Enterprise::Billing::Concerns::StripeV2ClientHelper
 
   # Cancel subscription using Stripe's V2 Billing Intent API
   # Creates a deactivate billing intent for the pricing plan subscription
@@ -29,11 +30,8 @@ class Enterprise::Billing::V2::CancelSubscriptionService < Enterprise::Billing::
     billing_cadence_id = fetch_billing_cadence_id(pricing_plan_subscription_id)
     store_next_billing_date(billing_cadence_id)
 
-    StripeV2Client.request(
-      :post,
-      '/v2/billing/intents',
-      build_deactivate_params(pricing_plan_subscription_id, billing_cadence_id),
-      stripe_api_options
+    create_billing_intent(
+      build_deactivate_params(pricing_plan_subscription_id, billing_cadence_id)
     )
   end
 
@@ -70,42 +68,6 @@ class Enterprise::Billing::V2::CancelSubscriptionService < Enterprise::Billing::
     }
   end
 
-  def reserve_billing_intent(billing_intent)
-    StripeV2Client.request(
-      :post,
-      "/v2/billing/intents/#{billing_intent.id}/reserve",
-      {},
-      stripe_api_options
-    )
-  end
-
-  def commit_billing_intent(billing_intent)
-    StripeV2Client.request(
-      :post,
-      "/v2/billing/intents/#{billing_intent.id}/commit",
-      {},
-      stripe_api_options
-    )
-  end
-
-  def retrieve_pricing_plan_subscription(subscription_id)
-    StripeV2Client.request(
-      :get,
-      "/v2/billing/pricing_plan_subscriptions/#{subscription_id}",
-      {},
-      stripe_api_options
-    )
-  end
-
-  def retrieve_billing_cadence(cadence_id)
-    StripeV2Client.request(
-      :get,
-      "/v2/billing/cadences/#{cadence_id}",
-      {},
-      stripe_api_options
-    )
-  end
-
   def update_account_status(_billing_intent)
     # Mark subscription as cancelling (will be cancelled at period end)
     # Store next_billing_date so the UI can show when the subscription ends
@@ -123,12 +85,4 @@ class Enterprise::Billing::V2::CancelSubscriptionService < Enterprise::Billing::
       message: 'Subscription cancellation initiated. It will be deactivated at the end of the current billing period.'
     }
   end
-
-  def stripe_api_options
-    { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-  end
-
-  def extract_attribute(object, key)
-    object.respond_to?(key) ? object.public_send(key) : object[key.to_s]
-  end
 end
diff --git a/enterprise/app/services/enterprise/billing/v2/change_plan_service.rb b/enterprise/app/services/enterprise/billing/v2/change_plan_service.rb
index 8e3ff74fe..9d97771a7 100644
--- a/enterprise/app/services/enterprise/billing/v2/change_plan_service.rb
+++ b/enterprise/app/services/enterprise/billing/v2/change_plan_service.rb
@@ -1,22 +1,23 @@
 class Enterprise::Billing::V2::ChangePlanService < Enterprise::Billing::V2::BaseService
   include Enterprise::Billing::Concerns::PlanFeatureManager
+  include Enterprise::Billing::Concerns::ProrationLineItemBuilder
+  include Enterprise::Billing::Concerns::StripeV2ClientHelper
+  include Enterprise::Billing::Concerns::PlanProvisioningHelper
 
-  # Change customer's pricing plan using Stripe's V2 Billing Intent API
-  # Creates a modify billing intent to migrate to a new pricing plan
+  # Change customer's pricing plan and/or seat quantity using invoice line items for proration
+  # Instantly applies the change and creates pending invoice line items
+  # for prorated charges that will be added to the next invoice
   #
-  # @param new_pricing_plan_id [String] The new Stripe pricing plan ID
-  # @param quantity [Integer] The quantity for the new plan
-  # @return [Hash] { success:, message: }
+  # @param new_pricing_plan_id [String, nil] The new Stripe pricing plan ID (nil to keep current plan)
+  # @param quantity [Integer] The seat quantity for the plan
+  # @return [Hash] { success:, message:, proration:, line_items: }
   #
-  def change_plan(new_pricing_plan_id:, quantity: 1)
-    return { success: false, message: 'Invalid quantity' } unless quantity.positive?
+  def change_plan(new_pricing_plan_id: nil, quantity: nil)
+    validation_error = validate_parameters(new_pricing_plan_id, quantity)
+    return validation_error if validation_error
 
     with_locked_account do
-      billing_intent = create_change_plan_intent(new_pricing_plan_id, quantity)
-      reserve_billing_intent(billing_intent)
-      commit_billing_intent(billing_intent)
-      update_account_plan(new_pricing_plan_id, quantity)
-      success_response(new_pricing_plan_id, quantity)
+      perform_subscription_change(new_pricing_plan_id, quantity)
     end
   rescue Stripe::StripeError => e
     { success: false, message: "Stripe error: #{e.message}" }
@@ -24,20 +25,71 @@ class Enterprise::Billing::V2::ChangePlanService < Enterprise::Billing::V2::Base
 
   private
 
-  def create_change_plan_intent(new_pricing_plan_id, quantity)
-    subscription_id = fetch_subscription_id
-    cadence_id = fetch_cadence_from_subscription(subscription_id)
-    store_next_billing_date(cadence_id)
-    plan_version = fetch_new_plan_version(new_pricing_plan_id)
-    lookup_key = fetch_plan_lookup_key(new_pricing_plan_id)
-    component_config = { lookup_key: lookup_key, quantity: quantity }
+  def validate_parameters(new_pricing_plan_id, quantity)
+    return { success: false, message: 'Must specify either new_pricing_plan_id or quantity' } if new_pricing_plan_id.nil? && quantity.nil?
+    return { success: false, message: 'Invalid quantity' } if quantity && !quantity.positive?
 
-    StripeV2Client.request(
-      :post,
-      '/v2/billing/intents',
-      build_change_plan_params(subscription_id, cadence_id, new_pricing_plan_id, plan_version, component_config),
-      stripe_api_options
+    # Validate customer has a default payment method using common service
+    payment_service = Enterprise::Billing::V2::InvoicePaymentService.new(account: account)
+    payment_method_validation = payment_service.validate_payment_method
+    return payment_method_validation unless payment_method_validation.nil?
+
+    nil
+  end
+
+  def perform_subscription_change(new_pricing_plan_id, quantity)
+    change_context = build_change_context(new_pricing_plan_id, quantity)
+    return no_change_response(change_context) unless change_required?(change_context)
+
+    execute_change(change_context)
+  end
+
+  def build_change_context(new_pricing_plan_id, quantity)
+    old_plan_id = custom_attribute('stripe_pricing_plan_id')
+    old_quantity = custom_attribute('subscribed_quantity').to_i
+    target_plan_id = new_pricing_plan_id || old_plan_id
+    target_quantity = quantity || old_quantity
+
+    {
+      old_plan_id: old_plan_id,
+      old_quantity: old_quantity,
+      target_plan_id: target_plan_id,
+      target_quantity: target_quantity,
+      plan_changed: old_plan_id != target_plan_id,
+      seats_changed: old_quantity != target_quantity
+    }
+  end
+
+  def change_required?(context)
+    context[:plan_changed] || context[:seats_changed]
+  end
+
+  def no_change_response(context)
+    plan_name = Enterprise::Billing::V2::PlanCatalog.definition_for(context[:target_plan_id])&.dig(:display_name) || 'Unknown Plan'
+    { success: false, message: "Subscription already has plan #{plan_name} with #{context[:target_quantity]} seat(s)" }
+  end
+
+  def execute_change(context)
+    # Create billing intent to update the Stripe subscription
+    billing_intent = create_change_plan_intent(context[:target_plan_id], context[:target_quantity])
+    reserve_billing_intent(billing_intent)
+    commit_billing_intent(billing_intent)
+
+    next_billing_date = custom_attribute('next_billing_date')
+    proration_data = calculate_proration(
+      old_plan_id: context[:old_plan_id],
+      new_plan_id: context[:target_plan_id],
+      old_quantity: context[:old_quantity],
+      new_quantity: context[:target_quantity],
+      next_billing_date: next_billing_date
     )
+    line_items = build_proration_line_items(context, proration_data)
+    invoice_result = create_and_charge_invoice(line_items)
+
+    update_account_plan(context[:target_plan_id], context[:target_quantity], next_billing_date)
+    provision_new_plan(context[:target_plan_id]) if context[:plan_changed]
+
+    success_response(context, proration_data, line_items, invoice_result)
   end
 
   def fetch_subscription_id
@@ -53,17 +105,17 @@ class Enterprise::Billing::V2::ChangePlanService < Enterprise::Billing::V2::Base
     end
   end
 
-  def fetch_new_plan_version(plan_id)
-    plan = retrieve_pricing_plan(plan_id)
-    extract_attribute(plan, :latest_version).tap do |version|
-      raise StandardError, "No version found for pricing plan #{plan_id}" if version.blank?
-    end
-  end
+  def create_change_plan_intent(new_pricing_plan_id, quantity)
+    subscription_id = fetch_subscription_id
+    cadence_id = fetch_cadence_from_subscription(subscription_id)
+    store_next_billing_date(cadence_id)
+    plan_version = fetch_new_plan_version(new_pricing_plan_id)
+    lookup_key = fetch_plan_lookup_key(new_pricing_plan_id)
+    component_config = { lookup_key: lookup_key, quantity: quantity }
 
-  def fetch_plan_lookup_key(plan_id)
-    Enterprise::Billing::V2::PlanCatalog.lookup_key_for_plan(plan_id).tap do |key|
-      raise StandardError, "Lookup key not found for pricing plan #{plan_id}" unless key
-    end
+    create_billing_intent(
+      build_change_plan_params(subscription_id, cadence_id, new_pricing_plan_id, plan_version, component_config)
+    )
   end
 
   def build_change_plan_params(subscription_id, cadence_id, plan_id, plan_version, component_config)
@@ -85,89 +137,81 @@ class Enterprise::Billing::V2::ChangePlanService < Enterprise::Billing::V2::Base
     }
   end
 
-  def reserve_billing_intent(billing_intent)
-    StripeV2Client.request(
-      :post,
-      "/v2/billing/intents/#{billing_intent.id}/reserve",
-      {},
-      stripe_api_options
-    )
-  end
-
-  def commit_billing_intent(billing_intent)
-    StripeV2Client.request(
-      :post,
-      "/v2/billing/intents/#{billing_intent.id}/commit",
-      {},
-      stripe_api_options
-    )
-  end
-
-  def retrieve_pricing_plan_subscription(subscription_id)
-    StripeV2Client.request(
-      :get,
-      "/v2/billing/pricing_plan_subscriptions/#{subscription_id}",
-      {},
-      stripe_api_options
-    )
-  end
-
-  def retrieve_pricing_plan(pricing_plan_id)
-    StripeV2Client.request(
-      :get,
-      "/v2/billing/pricing_plans/#{pricing_plan_id}",
-      {},
-      stripe_api_options
-    )
-  end
-
-  def retrieve_billing_cadence(cadence_id)
-    StripeV2Client.request(
-      :get,
-      "/v2/billing/cadences/#{cadence_id}",
-      {},
-      stripe_api_options
-    )
-  end
-
   def store_next_billing_date(cadence_id)
     cadence = retrieve_billing_cadence(cadence_id)
     @next_billing_date = extract_attribute(cadence, :next_billing_date)
+    update_custom_attributes({ 'next_billing_date' => @next_billing_date })
   end
 
-  def update_account_plan(new_pricing_plan_id, quantity)
-    attributes = {
-      'pending_stripe_pricing_plan_id' => new_pricing_plan_id,
-      'pending_subscription_quantity' => quantity,
-      'next_billing_date' => @next_billing_date
-    }
-
-    # Add plan name from catalog
-    plan_definition = Enterprise::Billing::V2::PlanCatalog.definition_for(new_pricing_plan_id)
-    attributes['plan_name'] = plan_definition[:display_name] if plan_definition
-
-    update_custom_attributes(attributes)
+  def fetch_new_plan_version(plan_id)
+    plan = retrieve_pricing_plan(plan_id)
+    extract_attribute(plan, :latest_version).tap do |version|
+      raise StandardError, "No version found for pricing plan #{plan_id}" if version.blank?
+    end
   end
 
-  def extract_plan_name(plan_definition)
-    # Extract plan name like "Startup", "Business", or "Enterprise" from display_name
-    plan_definition[:display_name].split.find { |word| %w[Startup Startups Business Enterprise].include?(word) }
+  def fetch_plan_lookup_key(plan_id)
+    Enterprise::Billing::V2::PlanCatalog.lookup_key_for_plan(plan_id).tap do |key|
+      raise StandardError, "Lookup key not found for pricing plan #{plan_id}" unless key
+    end
   end
 
-  def success_response(new_pricing_plan_id, quantity)
+  def calculate_proration(old_plan_id:, new_plan_id:, old_quantity:, new_quantity:, next_billing_date:)
+    old_plan_price = Enterprise::Billing::V2::PlanCatalog.definition_for(old_plan_id)&.dig(:base_fee) || 0.0
+    new_plan_price = Enterprise::Billing::V2::PlanCatalog.definition_for(new_plan_id)&.dig(:base_fee) || 0.0
+
+    Enterprise::Billing::V2::ProrationCalculator.calculate(
+      old_plan_price: old_plan_price,
+      new_plan_price: new_plan_price,
+      old_quantity: old_quantity,
+      new_quantity: new_quantity,
+      next_billing_date: next_billing_date
+    )
+  end
+
+  def create_and_charge_invoice(line_items)
+    # Return success with no invoice if no line items (negligible proration)
+    return { success: true, amount: 0.0, message: 'No charges due to negligible proration' } if line_items.empty?
+
+    # Use common invoice payment service
+    payment_service = Enterprise::Billing::V2::InvoicePaymentService.new(account: account)
+    payment_service.create_and_pay_invoice(
+      line_items: line_items,
+      description: 'Proration charges for plan/seat changes',
+      metadata: {
+        account_id: account.id.to_s,
+        type: 'proration'
+      }
+    )
+  end
+
+  def success_response(context, proration_data, line_items, invoice_result)
     {
       success: true,
-      pricing_plan_id: new_pricing_plan_id,
-      quantity: quantity,
-      message: 'Pricing plan changed successfully'
+      pricing_plan_id: context[:target_plan_id],
+      quantity: context[:target_quantity],
+      old_pricing_plan_id: context[:old_plan_id],
+      old_quantity: context[:old_quantity],
+      plan_changed: context[:plan_changed],
+      seats_changed: context[:seats_changed],
+      proration: proration_data,
+      line_items: line_items,
+      invoice: invoice_result,
+      total_proration_amount: proration_data[:net_amount],
+      message: build_change_message(context)
     }
   end
 
-  def stripe_api_options
-    { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-  end
+  def build_change_message(context)
+    plan_name = Enterprise::Billing::V2::PlanCatalog.definition_for(context[:target_plan_id])&.dig(:display_name) || 'Unknown Plan'
+    base_message = if context[:plan_changed] && context[:seats_changed]
+                     "Plan changed to #{plan_name} and seats updated to #{context[:target_quantity]}"
+                   elsif context[:plan_changed]
+                     "Plan changed to #{plan_name}"
+                   else
+                     "Seats updated from #{context[:old_quantity]} to #{context[:target_quantity]}"
+                   end
 
-  def extract_attribute(object, key)
-    object.respond_to?(key) ? object.public_send(key) : object[key.to_s]
+    "#{base_message} - billing intent committed and invoice line items created"
   end
 end
diff --git a/enterprise/app/services/enterprise/billing/v2/checkout_session_service.rb b/enterprise/app/services/enterprise/billing/v2/checkout_session_service.rb
index 739285721..45708616c 100644
--- a/enterprise/app/services/enterprise/billing/v2/checkout_session_service.rb
+++ b/enterprise/app/services/enterprise/billing/v2/checkout_session_service.rb
@@ -5,6 +5,7 @@
 #
 class Enterprise::Billing::V2::CheckoutSessionService < Enterprise::Billing::V2::BaseService
   include Enterprise::Billing::Concerns::PlanFeatureManager
+  include Enterprise::Billing::Concerns::StripeV2ClientHelper
 
   # Create a subscription checkout session
   #
@@ -53,14 +54,7 @@ class Enterprise::Billing::V2::CheckoutSessionService < Enterprise::Billing::V2:
   #
   def create_checkout_session
     customer_id = custom_attribute('stripe_customer_id')
-
-    session = StripeV2Client.request(
-      :post,
-      '/v1/checkout/sessions',
-      checkout_session_params(customer_id),
-      stripe_api_options
-    )
-
+    session = super(checkout_session_params(customer_id), api_version: checkout_stripe_version)
     build_success_response(session)
   end
 
@@ -126,11 +120,4 @@ class Enterprise::Billing::V2::CheckoutSessionService < Enterprise::Billing::V2:
       redirect_url: session_url
     }
   end
-
-  def stripe_api_options
-    {
-      api_key: ENV.fetch('STRIPE_SECRET_KEY', nil),
-      stripe_version: '2025-08-27.preview;checkout_product_catalog_preview=v1'
-    }
-  end
 end
diff --git a/enterprise/app/services/enterprise/billing/v2/invoice_payment_service.rb b/enterprise/app/services/enterprise/billing/v2/invoice_payment_service.rb
new file mode 100644
index 000000000..0c380904c
--- /dev/null
+++ b/enterprise/app/services/enterprise/billing/v2/invoice_payment_service.rb
@@ -0,0 +1,111 @@
+class Enterprise::Billing::V2::InvoicePaymentService < Enterprise::Billing::V2::BaseService
+  # Common service for creating invoices with line items and charging immediately
+  # Used by both TopupService and ChangePlanService
+  #
+  # @param line_items [Array<Hash>] Array of line items: [{ amount:, description:, metadata: }]
+  # @param description [String] Description for the invoice
+  # @param currency [String] Currency code (default: 'usd')
+  # @param metadata [Hash] Metadata for the invoice
+  # @return [Hash] { success:, invoice_id:, invoice_url:, amount:, status: }
+
+  # Validate that customer has a default payment method
+  # @return [Hash, nil] Returns error hash if validation fails, nil if success
+  def validate_payment_method
+    customer_id = custom_attribute('stripe_customer_id')
+    return { success: false, message: 'No Stripe customer ID found' } if customer_id.blank?
+
+    customer = Stripe::Customer.retrieve(customer_id, stripe_api_options)
+
+    if customer.invoice_settings.default_payment_method.nil? && customer.default_source.nil?
+      return {
+        success: false,
+        message: 'No default payment method found. Please add a default payment method before making a purchase.'
+      }
+    end
+
+    nil
+  rescue Stripe::StripeError => e
+    Rails.logger.error("Failed to check payment method: #{e.message}")
+    { success: false, message: "Error validating payment method: #{e.message}" }
+  end
+
+  # Create invoice with line items and charge immediately
+  #
+  # @param line_items [Array<Hash>] Line items: [{ amount: (cents), description:, metadata: }]
+  # @param description [String] Invoice description
+  # @param currency [String] Currency (default: 'usd')
+  # @param metadata [Hash] Invoice metadata
+  # @return [Hash] { success:, invoice_id:, invoice_url:, amount:, status: }
+  def create_and_pay_invoice(line_items:, description:, currency: 'usd', metadata: {})
+    customer_id = custom_attribute('stripe_customer_id')
+    invoice = create_invoice(customer_id, currency, description, metadata)
+    add_line_items_to_invoice(invoice.id, customer_id, line_items, currency)
+    finalize_and_pay_invoice(invoice.id)
+  rescue Stripe::StripeError => e
+    Rails.logger.error("Error creating invoice: #{e.message}")
+    { success: false, message: "Error creating invoice: #{e.message}" }
+  end
+
+  private
+
+  def create_invoice(customer_id, currency, description, metadata)
+    Stripe::Invoice.create({
+                             customer: customer_id,
+                             currency: currency,
+                             collection_method: 'charge_automatically',
+                             auto_advance: false,
+                             description: description,
+                             metadata: metadata.stringify_keys
+                           }, stripe_api_options)
+  end
+
+  def add_line_items_to_invoice(invoice_id, customer_id, line_items, currency)
+    line_items.each do |item|
+      Stripe::InvoiceItem.create({
+                                   customer: customer_id,
+                                   amount: item[:amount],
+                                   currency: currency,
+                                   invoice: invoice_id,
+                                   description: item[:description],
+                                   metadata: (item[:metadata] || {}).stringify_keys
+                                 }, stripe_api_options)
+    end
+  end
+
+  # Finalize invoice and pay it immediately
+  # @param invoice_id [String] Stripe invoice ID
+  # @return [Hash] { success:, invoice_id:, invoice_url:, amount:, status: }
+  def finalize_and_pay_invoice(invoice_id)
+    # Finalize the invoice
+    finalized_invoice = Stripe::Invoice.finalize_invoice(
+      invoice_id,
+      { auto_advance: false },
+      stripe_api_options
+    )
+
+    # Pay the invoice immediately if not already paid
+    if finalized_invoice.status == 'paid'
+      build_invoice_response(finalized_invoice)
+    else
+      paid_invoice = Stripe::Invoice.pay(invoice_id, {}, stripe_api_options)
+      build_invoice_response(paid_invoice)
+    end
+  rescue Stripe::StripeError => e
+    Rails.logger.error("Error finalizing/paying invoice: #{e.message}")
+    { success: false, message: "Error processing payment: #{e.message}" }
+  end
+
+  def build_invoice_response(invoice)
+    {
+      success: true,
+      invoice_id: invoice.id,
+      invoice_url: invoice.hosted_invoice_url,
+      amount: invoice.total / 100.0,
+      status: invoice.status
+    }
+  end
+
+  def stripe_api_options
+    { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
+  end
+end
diff --git a/enterprise/app/services/enterprise/billing/v2/pricing_plan_component_builder.rb b/enterprise/app/services/enterprise/billing/v2/pricing_plan_component_builder.rb
index 909b97112..c3a04ac14 100644
--- a/enterprise/app/services/enterprise/billing/v2/pricing_plan_component_builder.rb
+++ b/enterprise/app/services/enterprise/billing/v2/pricing_plan_component_builder.rb
@@ -1,4 +1,6 @@
 class Enterprise::Billing::V2::PricingPlanComponentBuilder < Enterprise::Billing::V2::BaseService
+  include Enterprise::Billing::Concerns::StripeV2ClientHelper
+
   def add_license_fee_component(plan, config)
     licensed_item = create_licensed_item(
       display_name: config[:licensed_item_display_name],
@@ -62,39 +64,24 @@ class Enterprise::Billing::V2::PricingPlanComponentBuilder < Enterprise::Billing
   private
 
   def create_licensed_item(display_name:, lookup_key:, unit_label:)
-    StripeV2Client.request(
-      :post,
-      '/v2/billing/licensed_items',
-      { display_name: display_name, lookup_key: lookup_key, unit_label: unit_label },
-      { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-    )
+    super({ display_name: display_name, lookup_key: lookup_key, unit_label: unit_label })
   end
 
   def create_license_fee(display_name:, unit_amount:, licensed_item_id:, lookup_key:)
-    StripeV2Client.request(
-      :post,
-      '/v2/billing/license_fees',
-      {
-        display_name: display_name,
-        currency: 'usd',
-        service_interval: 'month',
-        service_interval_count: 1,
-        tax_behavior: 'exclusive',
-        unit_amount: unit_amount.to_s,
-        licensed_item: licensed_item_id,
-        lookup_key: lookup_key
-      },
-      { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-    )
+    super({
+      display_name: display_name,
+      currency: 'usd',
+      service_interval: 'month',
+      service_interval_count: 1,
+      tax_behavior: 'exclusive',
+      unit_amount: unit_amount.to_s,
+      licensed_item: licensed_item_id,
+      lookup_key: lookup_key
+    })
   end
 
   def create_service_action(lookup_key:, credit_amount:, cpu_id:)
-    StripeV2Client.request(
-      :post,
-      '/v2/billing/service_actions',
-      service_action_params(lookup_key, credit_amount, cpu_id),
-      stripe_api_options
-    )
+    super(service_action_params(lookup_key, credit_amount, cpu_id))
   end
 
   def service_action_params(lookup_key, credit_amount, cpu_id)
@@ -119,44 +106,25 @@ class Enterprise::Billing::V2::PricingPlanComponentBuilder < Enterprise::Billing
     }
   end
 
-  def stripe_api_options
-    { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-  end
-
   def create_rate_card(display_name:)
-    StripeV2Client.request(
-      :post,
-      '/v2/billing/rate_cards',
-      {
-        display_name: display_name,
-        currency: 'usd',
-        service_interval: 'month',
-        service_interval_count: 1,
-        tax_behavior: 'exclusive'
-      },
-      { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-    )
+    super({
+      display_name: display_name,
+      currency: 'usd',
+      service_interval: 'month',
+      service_interval_count: 1,
+      tax_behavior: 'exclusive'
+    })
   end
 
   def create_metered_item(display_name:, lookup_key:, meter_id:)
-    StripeV2Client.request(
-      :post,
-      '/v2/billing/metered_items',
-      { display_name: display_name, lookup_key: lookup_key, meter: meter_id },
-      { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-    )
+    super({ display_name: display_name, lookup_key: lookup_key, meter: meter_id })
   end
 
   def add_rate(card_id:, item_id:, cpu_id:, value:)
-    StripeV2Client.request(
-      :post,
-      "/v2/billing/rate_cards/#{card_id}/rates",
-      {
-        metered_item: item_id,
-        custom_pricing_unit_amount: { id: cpu_id, value: value.to_s }
-      },
-      { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-    )
+    add_rate_to_card(card_id, {
+                       metered_item: item_id,
+                       custom_pricing_unit_amount: { id: cpu_id, value: value.to_s }
+                     })
   end
 
   def add_component(plan_id:, type:, data:, lookup_key:)
@@ -169,11 +137,6 @@ class Enterprise::Billing::V2::PricingPlanComponentBuilder < Enterprise::Billing
                { type: 'rate_card', rate_card: data, lookup_key: lookup_key }
              end
 
-    StripeV2Client.request(
-      :post,
-      "/v2/billing/pricing_plans/#{plan_id}/components",
-      params,
-      { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-    )
+    add_pricing_plan_component(plan_id, params)
   end
 end
diff --git a/enterprise/app/services/enterprise/billing/v2/pricing_plan_service.rb b/enterprise/app/services/enterprise/billing/v2/pricing_plan_service.rb
index c3a29819d..56d6c73d4 100644
--- a/enterprise/app/services/enterprise/billing/v2/pricing_plan_service.rb
+++ b/enterprise/app/services/enterprise/billing/v2/pricing_plan_service.rb
@@ -1,11 +1,8 @@
 class Enterprise::Billing::V2::PricingPlanService < Enterprise::Billing::V2::BaseService
+  include Enterprise::Billing::Concerns::StripeV2ClientHelper
+
   def create_custom_pricing_unit(display_name:, lookup_key:)
-    StripeV2Client.request(
-      :post,
-      '/v2/billing/custom_pricing_units',
-      { display_name: display_name, lookup_key: lookup_key },
-      { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-    )
+    super({ display_name: display_name, lookup_key: lookup_key })
   end
 
   def create_meter(display_name:, event_name:)
@@ -17,21 +14,11 @@ class Enterprise::Billing::V2::PricingPlanService < Enterprise::Billing::V2::Bas
       'customer_mapping[event_payload_key]' => 'stripe_customer_id',
       'value_settings[event_payload_key]' => 'value'
     }
-    StripeV2Client.request(
-      :post,
-      '/v1/billing/meters',
-      params,
-      { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-    )
+    super(params)
   end
 
   def create_pricing_plan(display_name:, lookup_key:, currency: 'usd', tax_behavior: 'exclusive')
-    StripeV2Client.request(
-      :post,
-      '/v2/billing/pricing_plans',
-      { display_name: display_name, currency: currency, tax_behavior: tax_behavior, lookup_key: lookup_key },
-      { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-    )
+    super({ display_name: display_name, currency: currency, tax_behavior: tax_behavior, lookup_key: lookup_key })
   end
 
   def create_complete_pricing_plan(config)
@@ -103,12 +90,7 @@ class Enterprise::Billing::V2::PricingPlanService < Enterprise::Billing::V2::Bas
   end
 
   def make_plan_version_live(plan_id)
-    StripeV2Client.request(
-      :post,
-      "/v2/billing/pricing_plans/#{plan_id}",
-      { live_version: 'latest' },
-      { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-    )
+    update_pricing_plan(plan_id, { live_version: 'latest' })
   end
 
   def build_plan_result(plan, cpu, meter)
diff --git a/enterprise/app/services/enterprise/billing/v2/proration_calculator.rb b/enterprise/app/services/enterprise/billing/v2/proration_calculator.rb
new file mode 100644
index 000000000..dacd2cc63
--- /dev/null
+++ b/enterprise/app/services/enterprise/billing/v2/proration_calculator.rb
@@ -0,0 +1,99 @@
+# rubocop:disable Style/ClassAndModuleChildren
+module Enterprise
+  module Billing
+    module V2
+      class ProrationCalculator
+        # Calculate prorated amounts for subscription changes
+        #
+        # @param old_plan_price [Float] Price per unit of the old plan
+        # @param new_plan_price [Float] Price per unit of the new plan
+        # @param old_quantity [Integer] Old quantity/seats
+        # @param new_quantity [Integer] New quantity/seats
+        # @param next_billing_date [String/Time] Next billing date (ISO 8601)
+        # @return [Hash] { credit_amount:, charge_amount:, net_amount:, days_remaining:, total_days: }
+        #
+        def self.calculate(old_plan_price:, new_plan_price:, old_quantity:, new_quantity:, next_billing_date:)
+          new(
+            old_plan_price: old_plan_price,
+            new_plan_price: new_plan_price,
+            old_quantity: old_quantity,
+            new_quantity: new_quantity,
+            next_billing_date: next_billing_date
+          ).calculate
+        end
+
+        def initialize(old_plan_price:, new_plan_price:, old_quantity:, new_quantity:, next_billing_date:)
+          @old_plan_price = old_plan_price.to_f
+          @new_plan_price = new_plan_price.to_f
+          @old_quantity = old_quantity.to_i
+          @new_quantity = new_quantity.to_i
+          @next_billing_date = parse_date(next_billing_date)
+          @current_date = Time.zone.now
+        end
+
+        def calculate
+          {
+            credit_amount: credit_amount,
+            charge_amount: charge_amount,
+            net_amount: net_amount,
+            days_remaining: days_remaining,
+            total_days: total_days,
+            proration_factor: proration_factor
+          }
+        end
+
+        private
+
+        def parse_date(date)
+          return date if date.is_a?(Time) || date.is_a?(DateTime)
+
+          Time.zone.parse(date.to_s)
+        rescue StandardError
+          raise ArgumentError, "Invalid next_billing_date format: #{date}"
+        end
+
+        # Credit from unused time on old plan
+        def credit_amount
+          @credit_amount ||= (@old_plan_price * @old_quantity * proration_factor).round(2)
+        end
+
+        # Charge for new plan for remaining time
+        def charge_amount
+          @charge_amount ||= (@new_plan_price * @new_quantity * proration_factor).round(2)
+        end
+
+        # Net amount to charge (positive) or credit (negative)
+        def net_amount
+          @net_amount ||= (charge_amount - credit_amount).round(2)
+        end
+
+        # Number of days remaining in current billing period
+        def days_remaining
+          @days_remaining ||= (@next_billing_date.to_date - @current_date.to_date).to_i
+        end
+
+        # Total days in the actual billing period (calculate from current cycle)
+        # This ensures proration factor never exceeds 1.0
+        def total_days
+          @total_days ||= begin
+            # Calculate the total days in this billing cycle
+            # Assume billing started one month ago from next_billing_date
+            billing_start = @next_billing_date - 1.month
+            ((@next_billing_date.to_date - billing_start.to_date).to_i)
+          end
+        end
+
+        # Fraction of billing period remaining
+        # This value should always be between 0.0 and 1.0
+        def proration_factor
+          @proration_factor ||= begin
+            factor = days_remaining.to_f / total_days
+            # Ensure factor never exceeds 1.0
+            [factor, 1.0].min.round(4)
+          end
+        end
+      end
+    end
+  end
+end
+# rubocop:enable Style/ClassAndModuleChildren
diff --git a/enterprise/app/services/enterprise/billing/v2/subscription_provisioning_service.rb b/enterprise/app/services/enterprise/billing/v2/subscription_provisioning_service.rb
index 66c76262d..dd6e418eb 100644
--- a/enterprise/app/services/enterprise/billing/v2/subscription_provisioning_service.rb
+++ b/enterprise/app/services/enterprise/billing/v2/subscription_provisioning_service.rb
@@ -1,5 +1,6 @@
 class Enterprise::Billing::V2::SubscriptionProvisioningService < Enterprise::Billing::V2::BaseService
   include Enterprise::Billing::Concerns::PlanFeatureManager
+  include Enterprise::Billing::Concerns::StripeV2ClientHelper
 
   def provision(subscription_id:)
     # Retrieve pricing plan subscription details from Stripe V2 API
@@ -77,15 +78,6 @@ class Enterprise::Billing::V2::SubscriptionProvisioningService < Enterprise::Bil
     reset_captain_usage
   end
 
-  def retrieve_pricing_plan_subscription(subscription_id)
-    StripeV2Client.request(
-      :get,
-      "/v2/billing/pricing_plan_subscriptions/#{subscription_id}",
-      {},
-      stripe_api_options
-    )
-  end
-
   def extract_pricing_plan_id(subscription)
     # Extract pricing_plan from the subscription object
     subscription.respond_to?(:pricing_plan) ? subscription.pricing_plan : subscription['pricing_plan']
@@ -163,8 +155,4 @@ class Enterprise::Billing::V2::SubscriptionProvisioningService < Enterprise::Bil
     # e.g., "Chatwoot Startup" -> "Startup"
     plan_definition[:display_name].split.find { |word| %w[Startup Startups Business Enterprise].include?(word) }
   end
-
-  def stripe_api_options
-    { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-  end
 end
diff --git a/enterprise/app/services/enterprise/billing/v2/topup_service.rb b/enterprise/app/services/enterprise/billing/v2/topup_service.rb
index 5cb829f7d..018b204b9 100644
--- a/enterprise/app/services/enterprise/billing/v2/topup_service.rb
+++ b/enterprise/app/services/enterprise/billing/v2/topup_service.rb
@@ -27,11 +27,10 @@ class Enterprise::Billing::V2::TopupService < Enterprise::Billing::V2::BaseServi
     return { valid: false, success: false, message: 'Unsupported topup amount' } unless topup_definition
     return { valid: false, success: false, message: 'Stripe customer not configured' } if stripe_customer_id.blank?
 
-    # Check if customer has a default payment method
-    unless customer_has_payment_method?
-      return { valid: false, success: false,
-               message: 'No default payment method found. Please add a default payment method before making a purchase.' }
-    end
+    # Check if customer has a default payment method using common service
+    payment_service = Enterprise::Billing::V2::InvoicePaymentService.new(account: account)
+    payment_method_validation = payment_service.validate_payment_method
+    return payment_method_validation.merge(valid: false) if payment_method_validation
 
     { valid: true, topup_definition: topup_definition }
   end
@@ -51,33 +50,40 @@ class Enterprise::Billing::V2::TopupService < Enterprise::Billing::V2::BaseServi
     { valid: true }
   end
 
-  def customer_has_payment_method?
-    customer = Stripe::Customer.retrieve(stripe_customer_id, stripe_api_options)
-    # Check if customer has a default payment method or any payment methods attached
-    customer.invoice_settings&.default_payment_method.present? || customer.default_source.present?
-  rescue Stripe::StripeError => e
-    Rails.logger.error("Failed to check payment method: #{e.message}")
-    false
-  end
-
   def process_topup_transaction(credits, amount_cents, currency, amount)
-    invoice = create_topup_invoice(currency)
-    return { success: false, message: 'Failed to create invoice' } unless invoice
-
-    invoice_item = create_topup_invoice_item(invoice.id, amount_cents, currency, credits)
-    return { success: false, message: 'Failed to create invoice item' } unless invoice_item
-
-    finalized_invoice = finalize_topup_invoice(invoice.id)
-    return { success: false, message: 'Failed to finalize invoice' } unless finalized_invoice
-
-    paid_invoice = pay_invoice(invoice.id)
-    return { success: false, message: 'Failed to pay invoice' } unless paid_invoice
+    line_items = build_topup_line_items(credits, amount_cents)
+    invoice_result = charge_topup_invoice(line_items, currency)
+    return invoice_result unless invoice_result[:success]
 
     credit_grant = create_stripe_credit_grant(amount_cents, currency, credits)
     return { success: false, message: 'Failed to create credit grant in Stripe' } unless credit_grant
 
-    # Credits will be added by webhook when Stripe sends billing.credit_grant.created event
-    build_success_response(credits, amount, currency, invoice.id, credit_grant['id'])
+    build_success_response(credits, amount, currency, invoice_result[:invoice_id], credit_grant['id'])
+  end
+
+  def build_topup_line_items(credits, amount_cents)
+    [{
+      amount: amount_cents,
+      description: "Credit Topup: #{credits} credits",
+      metadata: {
+        account_id: account.id.to_s,
+        credits: credits.to_s,
+        topup: 'true'
+      }
+    }]
+  end
+
+  def charge_topup_invoice(line_items, currency)
+    payment_service = Enterprise::Billing::V2::InvoicePaymentService.new(account: account)
+    payment_service.create_and_pay_invoice(
+      line_items: line_items,
+      description: 'Credit top-up purchase',
+      currency: currency,
+      metadata: {
+        account_id: account.id.to_s,
+        topup: 'true'
+      }
+    )
   end
 
   def build_success_response(credits, amount, currency, invoice_id, credit_grant_id)
@@ -92,60 +98,6 @@ class Enterprise::Billing::V2::TopupService < Enterprise::Billing::V2::BaseServi
     }
   end
 
-  # Create Invoice following Stripe UBB Integration Guide
-  def create_topup_invoice(currency)
-    Stripe::Invoice.create(
-      {
-        customer: stripe_customer_id,
-        currency: currency,
-        collection_method: 'charge_automatically',
-        auto_advance: false, # We'll finalize it manually
-        metadata: {
-          account_id: account.id.to_s,
-          topup: 'true'
-        }
-      },
-      stripe_api_options
-    )
-  end
-
-  # Create Invoice Item with topup amount
-  def create_topup_invoice_item(invoice_id, amount_cents, currency, credits)
-    Stripe::InvoiceItem.create(
-      {
-        customer: stripe_customer_id,
-        amount: amount_cents,
-        currency: currency,
-        invoice: invoice_id,
-        description: "Credit Topup: #{credits} credits",
-        metadata: {
-          account_id: account.id.to_s,
-          credits: credits.to_s,
-          topup: 'true'
-        }
-      },
-      stripe_api_options
-    )
-  end
-
-  # Finalize Invoice for payment
-  def finalize_topup_invoice(invoice_id)
-    Stripe::Invoice.finalize_invoice(
-      invoice_id,
-      { auto_advance: false }, # We'll pay it explicitly
-      stripe_api_options
-    )
-  end
-
-  # Pay the invoice explicitly
-  def pay_invoice(invoice_id)
-    Stripe::Invoice.pay(
-      invoice_id,
-      {},
-      stripe_api_options
-    )
-  end
-
   # Create Credit Grant in Stripe using monetary amount (not custom_pricing_unit)
   # Following Stripe UBB Integration Guide section 8
   def create_stripe_credit_grant(amount_cents, currency, credits)
diff --git a/enterprise/app/services/enterprise/billing/v2/webhook_handler_service.rb b/enterprise/app/services/enterprise/billing/v2/webhook_handler_service.rb
index 32c14a8b1..ee569b217 100644
--- a/enterprise/app/services/enterprise/billing/v2/webhook_handler_service.rb
+++ b/enterprise/app/services/enterprise/billing/v2/webhook_handler_service.rb
@@ -1,4 +1,6 @@
 class Enterprise::Billing::V2::WebhookHandlerService
+  include Enterprise::Billing::Concerns::StripeV2ClientHelper
+
   def perform(event:)
     @event = event
     return { success: false, message: 'Event is required' } if @event.blank?
@@ -37,20 +39,10 @@ class Enterprise::Billing::V2::WebhookHandlerService
   end
 
   def fetch_customer_id_from_subscription(subscription_id)
-    subscription = StripeV2Client.request(
-      :get,
-      "/v2/billing/pricing_plan_subscriptions/#{subscription_id}",
-      {},
-      stripe_api_options
-    )
+    subscription = retrieve_pricing_plan_subscription(subscription_id)
     return nil unless subscription&.billing_cadence
 
-    cadence = StripeV2Client.request(
-      :get,
-      "/v2/billing/cadences/#{subscription.billing_cadence}",
-      {},
-      stripe_api_options
-    )
+    cadence = retrieve_billing_cadence(subscription.billing_cadence)
     cadence.payer&.customer
   end
 
@@ -65,8 +57,4 @@ class Enterprise::Billing::V2::WebhookHandlerService
       .new(account: account)
       .refresh
   end
-
-  def stripe_api_options
-    { api_key: ENV.fetch('STRIPE_SECRET_KEY', nil), stripe_version: '2025-08-27.preview' }
-  end
 end