Separating free image credits from paid credits after Fincra checkout

We are reviewing how a possible Fincra checkout would work for whisk ai, an AI image remix service with free starter credits and paid image-generation plans. Fincra is not integrated today.

A generation can cost 10 credits. We need to keep free trial allowances distinct from paid credits when grants, failed jobs, and refunds are reconciled.

1. After a successful Fincra payment, which webhook and transaction reference should be used for exactly-once paid-credit fulfillment?

2. If the same user still has free starter credits, should the paid-credit grant and consumption order live entirely in our own ledger, with Fincra recording payment only?

3. If a paid generation fails or a payment is reversed, which Fincra events should drive the financial reconciliation while our own ledger restores only the affected usage credits?

Any Fincra event examples for this split free-and-paid credit setup would help us assess the integration.