If a customer overpays, we automatically present a refund form on the invoice itself after our system approves the payment. As such, in most cases, you don’t have to do anything at all.
However, if, by any chance, a customer did not see or turned off the refund window, you should redirect him to CoinGate support at email@example.com and inform to provide us with Order ID, email address (if specified during the payment) or output address of cryptocurrency wallet. When your customer contacts us, we will resend the refund form to him.
Be mindful that refunds can take up to 48 hours to issue.