It shows the addons but doesn’t allow me to add the addons to the box.

Your product box must be unpurchasable according to woocommerce.

Steps to follow in this scenario:

1. Check if there is an add to cart button on the page.
2. 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.