Bump products stay inactive until a main product is also present on the form. Add the main product first, then the bump product becomes available.
Open your form in the Form Builder and select the Sell Products element.
Click Add Product and choose Main Product as the product type. If the product doesn't exist yet, use the create-product link in the product selector to set it up.
Click Add Product again, select your product, and choose Bump Product as the product type.
For where the Sell Products element lives in the builder, see Add products to a form.