This POST endpoint reverses, or closes, a pay-in transaction for the user and payin token provided.
Both the effect and the conditions depend on how the pay-in was funded:

• Temporary bank account (ACH/wire) or issued crypto deposit wallet: reversing closes the deposit account so that it accepts no further deposits. This is permitted even after deposits have already settled — deposits already received are unaffected and remain recorded.
• Card authorization: reversing releases the card authorization. This is only permitted while the authorization has not been captured. A captured authorization represents settled funds and cannot be reversed; use the refund flow instead.

A pay-in that has already been reversed, or that is in a non-reversible state for its funding type, returns a 400.
On success the pay-in transitions to CANCELLED and the updated pay-in object is returned.