One reason why the cart campaign, in the Ultimate Sales Boost app, may not be displayed is because you are using a drawer cart.
USB currently only supports showing the campaign on a cart page type. It doesn't support the popup and drawer cart.
Most themes have "cart page" available, and usually, you can change the type of the cart in the Theme settings > Cart > Cart type.
If you cannot find the option, please contact the theme developers. They are the best persons to help.