Your product box must be unpurchasable according to woocommerce.
Steps to follow in this scenario:
- Check if there is an add to cart button on the page.
- Check if the box is set some price.
- If not then the box is not purchasable and you can’t add it to the cart.
- For this set a regular price to the box.
- If you want to set the pricing type as Only the addon price then set the regular price as 0. and set the pricing type to Only add-on products price.