This happens if you don't pay the full amount, before the countdown on the invoice ends. This can sometimes happen due to an additional small commission from the payment provider, which is paid and the order itself becomes underpaid by a small amount of this commission.
Coingate: If an order is underpaid, we don't receive any payment from our payment provider, so please use this link to request a refund: https://support.coingate.com/hc/en-us/requests/new. Coingate should issue a refund within 48 hours of your request. If the refund was not issued within this period of time, then you can contact the payment provider Coingate again.
MixPay: If an order is underpaid, we don't receive any payment from our payment provider, so please use this link to request a refund: https://help.mixpay.me/en/articles/6836092-how-to-contact-customer-service. Or just write to: customer@mixpay.me.
If you have paid for an order using another payment provider and suspect that the order is underpaid, please contact our customer support team by creating a support ticket.