Article R213-11 of the French Code of civil enforcement procedures
When an organisation responsible for paying family benefits acts on behalf of a maintenance creditor, it shall notify the request for direct payment to the third party mentioned in article L. 213-1 by registered letter with acknowledgement of receipt which includes, on pain of nullity, the information provided for in the second paragraph of article R. 213-1 as well as the terms and conditions for the payment of unpaid instalments….