As stated above, I would like to know how to create an optional addon for my products. The add on can not be available or visible anywhere else in the store. I would also need the inventory to be counted and the addon not offered when it is out of stock. Are there any apps for this on shopify?
I have seen apps such as SellUp, but they are very vague when it comes to if the addon has to be visible elsewhere or if they count inventory.