There are 2 buttons on your screenshot: Wishlist and Add to cart. Add to cart button does not display in our theme because your product is the variable product and you need to choose the variation before adding to the cart. Unfortunately, we don’t have the option of choosing variations from the sticky panel. Add to cart button in the the sticky panel available for the simple products only. So, you can submit refund request for our theme here https://themeforest.net/refund_requests/new if you want to choose another theme that has such option. We don’t have it unfortunately.