I have created a new add-on that does not appear during the creation of a reservation. Why is that?

There are three possible reasons for this:

1. The add-on setting 'Available to Staff' has not been enabled
2. The add-on setting 'Allow orders on' setting has not been enabled to allow for the add-on to selected for 1-night reservations
3. The stay date range of your booking is not within the add-on validity period