How can I make a refund to my customer?
If it is a standard refund (your customer decided to return the merchandise) you should refund the customer like you refund all your other customers, that is, in the currency in which you are receiving payouts from CoinGate.
In the invoice was underpaid, overpaid, or if the invoice expired before the payment made it to the payment address, the refund can be requested directly from the invoice by customers themselves. Please see here for more details.
If the refund form is not available on the invoice, please to request a refund.