If you are using the SmartHOTEL payment Provider, Adyen, this is how you refund a payment.
Log in to your Customer Area.
Go to Transactions > Payments, and select the PSP reference of the payment that you want to refund.
This opens the Payment Details page.
Select Manage payment in the upper right corner of the page, then Refund payment.
Confirm the details of the refund:
Amount: The amount you want to refund. This must be either the same or, in case of a partial refund, less than the captured amount.
Reference: Your reference for the refund request.
Select the Refund this payment checkbox, then select the Refund payment button in the lower right corner of the page.