Prorated refunds for annual photo-editing credits with Fincra

We are assessing a possible Fincra payment flow for ai photo editor, a browser-based photo-editing and image-generation service. Its annual plans issue a fixed pool of credits up front, and failed generations return usage credits. Fincra is not integrated today.

1. For an annual purchase, which confirmed Fincra payment event should trigger the initial credit pool, and which identifier prevents duplicate fulfillment after webhook retries?

2. If an image-generation job fails and application credits are returned, should that remain an internal ledger event rather than a payment refund?

3. If a customer later requests a prorated cash refund for unused annual credits, can a partial refund be tied to the original Fincra transaction while the consumed credits remain recorded separately?

Pointers to the relevant payment and refund events, including sandbox tests, would help us evaluate this flow.