If you’re trying to make it properly have a max inventory slot system, I recommend using an IntValue which is the main part of that UI. When you click on one of the buttons to equip it, tell the server to Add 1 onto the IntValue. When the player unequips, tell the server to subtract 1 from the IntValue to act as 1 slot being freed up.
By the looks of it, the max inventory size is 4, so make your the server has that information as well stored in a variable. It would compare the number on the players IntValue, and if it’s equal to 4 already, then it won’t let them equip the tool.
You just gotta make sure you incorporate the math so the server knows the limit.