fix: multiple same payment methods stored even though logic in place for SEPA

[mehul0810]

Bug Report

User Story

As a user, I want to store a SEPA payment method once if the same is used for the second time so that it doesn't create an unnecessary payment method for the Stripe customer.

Related to https://github.com/impress-org/givewp/issues/4313

Current Behavior

Currently, when I use same IBAN account number for one user for multiple donations then multiple payment methods are created for the same user having same IBAN account number

Expected Behavior

I expect to discuss this scenario with Stripe developers as to when fetching the payment method list via API I am getting empty results even though there is an IBAN account number payment method due to which this issue is present.

Bug Type

• [ ] This bug describes functionality that once worked as expected in version X.X.X.
• [ ] This bug describes functionality that never worked as expected.
• [x] I am not sure whether this functionality ever worked as expected.

Acceptance Criteria

• [ ] No multiple entries of payment method under customer when same IBAN account number is used for multiple donations of same email.

[jonwaldstein]

I see we're using the setup_future_usage payment intent argument for Stripe (SEPA) which in theory should work.

There is also these (newer) docs around the subject.

https://stripe.com/docs/payments/sepa-debit/set-up-payment

@DevinWalker do you have any recollection of this being an issue with customers? or is this just an optimization we've identified?

@kjohnson did you happen to run into this when you were migrating SEPA to the gateway api?

[JoshuaHungDinh]

No recent feedback. Related to https://github.com/impress-org/givewp/issues/4313