There are two distinct ways to place an offer in the drawer: directly in the slide-out drawer itself, or inside an embedded widget within the drawer body — useful if your theme's drawer already has its own content sections and you want the offer to sit inside one of them rather than appended to the drawer as a whole. Both are full-capability contexts, identical to the cart page in what they support.
UpsellPlus also ships a complete cart drawer of its own, which can replace a theme's native drawer rather than adding offers into it — relevant if a theme's drawer is difficult to extend, or if you'd rather not maintain two drawer implementations side by side.
The one practical wrinkle specific to this surface: because the drawer is a persistent UI element that doesn't reload with the page, some themes need a small AJAX-refresh snippet so the drawer actually reflects an accepted offer immediately rather than only on the next full cart update.