Cancels a payment that has not yet been sent for processing. A payment going through our checks, or already sent to the payment processor or bank, cannot be cancelled and returns 422; a payment that is already cancelled returns 409. An approved INR payment cannot be cancelled through the API and returns 422; contact IFX operations. The payment must be visible to the caller's auth group (a member's, or a member's sub-account's, payment); anything else returns 404. reason is required and must be one of: incorrect_amount, incorrect_payee, payment_not_required.