I cannot use the card at unmanned petrol stations or toll roads

Unmanned gas installations are an exception as they work with different pre-authorization systems per country, which may cause some issues. Since the merchant does not yet know the amount for which you want to refuel when you enter your card, an authorization is requested for a standard amount. In most cases, the amount is EUR 125.
If your balance is not high enough for this amount, the authorization will be rejected.
Then the transaction is aborted at the pump because no authorization has been obtained.

Toll roads can also be an issue depending on the merchant since not all toll roads are connected to the internet and can check in advance whether the card is active or contains money.

As a result, many toll roads choose not to accept prepaid cards at all.