With the Favourites addon, a new shortcode is available. The shortcode allows you to display a button to add or remove a listing from the bookmarks, anywhere on your site.
When used without an ID parameter, the button will automatically display only on the single listing page allowing users to add/remove the listing currently being displayed.
When using the ID parameter, you can specify the listing that users can add or remove from their bookmarks.
Please note: if you've specified an ID but the button does not display, it means the ID does not belong to a listing.