I think I must just be doing something fairly simple but wrong in trying to set up the item slot upgrades plugin. I've watched the youtube preview several times and I think I doing it right but it doesn't work.
Spoiler

Here is the script below ITEM CORE

Here is the item page where I have it able to be used on all weapon types and give +5 atk.
Here is a custom weapon I want to upgrade
Here I am in game after getting the item from a chest

Looking good so far, but I select upgrade shovel and then I can't use the item.

It just makes the error noise when I hit enter and also when I try to use the item it just goes to the character select screen and makes the error noise if I try to select a character.