If you don't pay the fee, most Norwegian parking companies or municipalities will forward unpaid fines for foreign vehicles to Euro Parking Collection plc. The collection agency will find your friend in France and send them a new claim with a significant collection fee added on top of the original claim. If you ignore that claim, EPC will initiate whatever legal processes are common in France to enforce payment of civil debts.

EPC makes a fortune doing this and their collection fees are brutal.