Refunds a fulfilled order, fully or partially. Requires scope orders:write.

Example request:

{ "amount": 300.00, "reason": "Customer return" }

The maximum refundable amount is fulfilledAmount − alreadyRefundedAmount.

Errors: 400 INVALID_STATUS if the order can't be refunded in its current state,
400 INVALID_AMOUNT if amount is zero or negative,
400 AMOUNT_EXCEEDED if amount exceeds the refundable balance,
403 FORBIDDEN if the API key lacks orders:write,
404 NOT_FOUND if the order doesn't exist or isn't yours.