At some gas stations or offline terminals on tolls, a minimum amount is required.
Service Stations: If an automated pay station, the driver requests a pre authorization for a maximum amount (between 70 € and 120 € in general) before it will work. The controller checks that you have enough balance on your card to perform the operation. After refueled, the trader does not automatically readjusts the amount of the initial authorization granted: the provision recorded in your account by the bank is kept at its maximum until the merchant sends the actual amount the bank at the end of the day. If you check your account at this time interval, then you will see between operations, provision, which need not necessarily correspond with the purchase made, and will refund the difference to your advantage if any.
Tolls: Tolls do not have the possibility to verify the account balance in real time, so the card could be rejected.