Returns money from a successful payment to the customer's card, through Pay.on. You can refund all of it or part of it.

• Applies to: a successful db (debit) or cp (capture). On a pre-authorised order, refund the cp, not the pa. A pa whose hold wasn't captured has nothing to refund: reverse it instead.
• Partial refunds: send amount. You can refund again until nothing is left. refundable_amount on the payment shows how much remains.
• Afterwards: the refund is a new rf payment with its own id. Its original_reference_id is the refunded payment's original_id. Once refunds add up to the full amount, the original payment's refunded is true.
• The currency is always the payment's. You can't change it.

A refund can't be undone.