Adding Enchants to Weapon Problem

So, Ive been trying to work on making a custom enchant table, that when a weapon is in the first slot, you can click a button, and it will add the enchant to the weapon in the second slot. However, when Im making the procedure for adding the enchant to the provided item, it says there's an item stack dependency problem. Does someone have an enchant procedure where this doesn't happen?

Thanks