Add donate-on-failure payment flag support

[Kingsman-99]

Labels: complexity: high

Update the SDK pay() method to accept a donateOnFailure boolean flag. When true, the payment is marked in the contract so that if the invoice fails to reach its goal, the funds are donated rather than refunded.

Acceptance criteria:

• pay({ invoiceId, amount, donateOnFailure }) passes the flag to the contract
• donateOnFailure defaults to false
• getPaymentHistory returns the flag per payment
• TypeScript type updated on PaymentOptions

---

[Osifowora]

@Osifowora has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

​Hi maintainer, I would love to work on this issue. I can get started on it right away.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Osifowora to this issue.

[modrispath]

@modrispath has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I'd like to work On it.

I'll update pay() to accept donateOnFailure (defaulting to false) on PaymentOptions, pass it through to the contract call, and make sure getPaymentHistory returns the flag per payment entry. TypeScript types updated throughout, with tests covering both flag states. Ready to go if assigned.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @modrispath to this issue.