## Description
When a customer downgrades from Enterprise to Business, they may retain
unused Stripe credit balance. During an AI credits topup,
Stripe::Invoice.finalize_invoice auto-applies that credit balance to the
invoice. If the credit balance fully covers the invoice amount, Stripe
marks it as paid immediately upon finalization. Calling
Stripe::Invoice.pay on an already-paid invoice throws an error, breaking
the topup flow.
This fix retrieves the invoice status after finalization and skips the
pay call if Stripe has already settled it via credits.
## Type of change
Please delete options that are not relevant.
- [ ] Bug fix (non-breaking change which fixes an issue)
## How Has This Been Tested?
Tested against Stripe test mode with the following scenarios:
- Full credit balance payment: Customer has enough Stripe credit balance
to cover the entire invoice. Invoice is marked paid after
finalize_invoice — pay is correctly skipped. Credits are fulfilled
successfully.
- Partial credit balance payment: Customer has some Stripe credit
balance but not enough to cover the full amount. Invoice remains open
after finalization — pay is called and charges the remaining amount to
the default payment method. Credits are fulfilled successfully.
- Zero credit balance (normal payment): Customer has no Stripe credit
balance. Invoice remains open after finalization — pay charges the full
amount. Credits are fulfilled successfully.
## Checklist:
- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules
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