How do I refund a payment?
Call refundPayment from your backend (or use the Refund action on the user's page in the console) — refunds are full, only COMPLETED payments qualify, and the payment moves to REFUNDED. There is no client-side route; end users can't refund themselves.
Revoke whatever the payment granted before you refund: refunds you initiate don't fire a trigger back into your system.