We strongly suggest using the /reversals endpoint for its functionality and enhanced flexibility when dealing with refunds (the /refunds endpoint is still supported).
A reversal will dynamically orchestrate a cancellation or refund based on the status of settlement process. A cancellation occurs if the transfer has not been settled. A refund occurs if the transfer is in the process of settling, or has already been settled.
A reversal cannot exceed the original transfer amount, and once the reversal process has started, it cannot be cancelled.