confirmRefund
Confirms an in-person refund after the refund payment method has been collected.
After confirming, the SDK will either call the RefundCallback's onSuccess method with a Refund object, or the onFailure method with a TerminalException object.
Your app should inspect the TerminalException to decide how to proceed.
Return
A Cancelable that allows the operation to be canceled when the SDK is not waiting for a network response.
Parameters
callback
The callback that will be called when the operation completes.