fix(billing): reconcile invoice default payment method by currency, drop default_source shortcut

config/locales/en.yml

@@ -169,7 +169,7 @@ en:
       invalid_option: Invalid topup option
       plan_not_eligible: Top-ups are only available for paid plans. Please upgrade your plan first.
       stripe_customer_not_configured: Stripe customer not configured
-      no_payment_method: No payment methods found. Please add a payment method before making a purchase.
+      no_payment_method: No payment method available for your billing currency. Please add a card before making a purchase.
     billing:
       currency_required: Currency is required
       currency_switch_unavailable: Currency switching is not available for this account

enterprise/app/services/enterprise/billing/default_payment_method_reconciler.rb

@@ -1,16 +1,13 @@
 # Ensures the customer's default Stripe payment method can actually bill the given currency. PIX/boleto
 # are BRL-only, so when an account moves to a currency they can't pay we drop them as the default and
 # pick a compatible method (a card) if one is attached. Incompatible methods stay attached for later.
+# Keyed off invoice_settings.default_payment_method, since that's what Stripe Billing charges.
 class Enterprise::Billing::DefaultPaymentMethodReconciler
   pattr_initialize [:account!, :currency!]
 
   # Returns the id of a currency-compatible default payment method, or nil if none is available.
   def reconcile
-    customer = Stripe::Customer.retrieve(stripe_customer_id)
-    # Legacy card sources are currency-agnostic.
-    return customer.default_source if customer.default_source.present?
-
-    current_default = customer.invoice_settings.default_payment_method
+    current_default = current_default_payment_method
     return current_default if compatible?(payment_methods.find { |method| method.id == current_default })
 
     compatible = payment_methods.find { |method| compatible?(method) }
@@ -22,6 +19,10 @@ class Enterprise::Billing::DefaultPaymentMethodReconciler
 
   private
 
+  def current_default_payment_method
+    Stripe::Customer.retrieve(stripe_customer_id).invoice_settings.default_payment_method
+  end
+
   def payment_methods
     @payment_methods ||= Stripe::PaymentMethod.list(customer: stripe_customer_id, limit: 100).data
   end