A Payment transaction can fail for a number of reasons.
It may be declined by your payment provider because of insufficient funds or passed credit limit. In these cases you should contact your payment provider (eg PayPal at https://www.paypal.com/be, or your card issuer).
It may fail because of a technical issue, in which case we suggest you wait a few seconds and try a second time. If it fails again we recommend that you use another payment method (by card at the pump or inside the shop) as there may be an issue with the connection to the pump.