Refund a guest's MyFatoorah payment

Sends a real refund to the guest's card through MyFatoorah: all that is left of the payment, amountCents of it, or the itemIds a payment made by items paid for, plus the guest's QR tip on it in the share of the payment refunded, given back as a negative tip row once MyFatoorah returns it. Answers pending once MyFatoorah accepted it, scheduled when its balance can't fund it yet (sent again daily), or unknown when it never answered (looked up before anything is resent). Refused with BAD_REQUEST and refusal notMyFatoorah for a payment not made through MyFatoorah, BAD_REQUEST and refusal overLimit for more than is left of it, CONFLICT and refusal inDoubt while its last refund is still unconfirmed, and PRECONDITION_FAILED when the business has no MyFatoorah connection. A retried idempotencyKey returns the same refund.