For the $3.99 one, it just becomes a bundle when ordered together. Also works with six piece nuggets. I’ve seen it on the menu in the store but it’s not incredibly prominent. And, in the app it’s basically just undocumented and the price drops when they’re both in your cart. It also doesn’t count as a promo in the app, so you can order more than one bundle and even use a promo with it as well.

https://imgur.com/a/2OOF8Fm