Mouse unlock script for FPS not working?

So im making a FPS game right now and you should be able to switch teams. The problem is its locked in first person and i need you need to unlock the Mouse in order to press the "Change Team" Button. I thought about making it modal it works but it doesn't really work mit my fps since you need to hold right click to look around in first person and i dont want that. I want to lets say Press M to unlock the Mouse and then press M again to lock it

Im pretty new to scripting so i made this:

local uis = game:GetService("UserInputService")
local rs = game:GetService("RunService")
local debounce = false

wait(1)
game:GetService("UserInputService").InputBegan:Connect(function(input)
    if input.KeyCode == Enum.KeyCode.M and debounce == false then
        debounce = true
        uis.MouseBehavior = Enum.MouseBehavior.LockCenter


    elseif input.KeyCode == Enum.KeyCode.M and debounce == true then
        debounce = false
        uis.MouseBehavior = Enum.MouseBehavior.Default
    end 
end)

But that doesnt work and i dont know why