French holiday rentals must display their registration number on their listings, and your own website is a listing. Once entered, it appears automatically.
Obtaining it
Your town hall issues it after a declaration. Many now have an online form. Some municipalities also require a change-of-use authorisation — a separate procedure.
Entering it
Dashboard → My website → Legal information → Registration number.
What must appear beside it
The maximum capacity and the cancellation conditions, both readable before booking, not only in a document sent afterwards. Both are generated from your property and booking settings.
Several properties
Each property has its own number: enter it on each property's page. Reusing the number of another property is an irregularity rather than a shortcut, and it is the kind of detail a municipal inspection looks at first.
If you do not have the number yet
Put your website online without it: an empty field simply displays nothing. Add it as soon as the town hall answers, and it appears everywhere it is needed at once — the property page, the booking summary and the confirmation e-mail — without you editing anything else.