This is an amount that is added to the toll if an official employee finds that the toll has not been paid (if the payment of the toll has not been made within 72 hours of your trip). 

This amount is set at €90 by the Code of Criminal Procedure.

However, for violations recorded in the context of a free-flow toll system, the fixed penalty will be reduced to €10 if you correct your situation within 15 days of the date on which the payment notice is sent.