Why won't the "purchase" function in my shop gui/physical store work?

The way my shop works is there's a large room with the item you can buy. Next to each item is a platform that opens a gui to purchase it. When you press Z, it should buy the item. When you press X, it should close the gui. Z isn't working. Here is my script.

local UserInputService = game:GetService("UserInputService")
local plr = game.Players.LocalPlayer

local function onInputBegan(input, gameProcessed)

    if input.KeyCode == Enum.KeyCode.Z and not gameProcessed then -- added a check for gameprocessed incase they were writing in chat

        if plr.leaderstats.Cash.Value >=20 then
            plr.leaderstats.Cash.Value = plr.leaderstats.Cash.Value - 20

            game.ReplicatedStorage.Library.AssaultRifle:Clone().Parent = plr:WaitForChild('Backpack')
        end

    end

end

UserInputService.InputBegan:Connect(onInputBegan)