If you underpaid your invoice, you will see the amount of cryptocurrency that you sent, as well as the amount that is still left to pay on the invoice. Simply make the second transaction to cover the underpaid amount before the invoice expires.
Once you make sufficient payment, your transaction will be confirmed. You will see a confirmation window with your Transaction IDs on the invoice.
If the CoinGate invoice got expired, a refund form will show up on the invoice. Once it does, fill in the necessary details and request a refund. We will process it manually within 48 hours.