The most common reasons add-on products may not display is the root category having been disabled.

To check this, navigate to Products > Products > Website Products, then in the list of categories to the left sidebar, simply make sure the very top one called Categories is checked/active. It should look like this:

If this is checked and your add-ons are still not showing, please contact us at 415-906-2850 x2 or support@floranext.com.