There is no automatic fine: the prefect may issue formal notice requiring you to report within 3 months, then publish the unheeded notice on a State website. The €1,500 or €7,500 fine concerns failure to meet targets, following an action programme procedure. Since 1 July 2026, the OPERAT certificate is also displayed and attached to sales and leases, making missing reports visible.
Read the source article: French Tertiary Decree and BACS: landlord and tenant duties