How can I find every Billboard Gui in the PlayerGui using ClassName? [UNSOLVED]

Hey, guys. I am trying to make a script that finds every single Billboard Gui inside a player's PlayerGui using ClassName, and making them enabled when the player presses the 'e' key. I tried the following inside a localscript, inside the StarterPack, but it doesn't seem to be working. If anyone can teach me the answer to this problem, I would gladly appreciate it!

Player = script.Parent.Parent
mouse = Player:GetMouse()

function onKeyDown(key)
key = key:lower()
    if script.Open.Value == false then
        if key == "e" then
            gui = Player.PlayerGui
            for _,  gui in ipairs(part:GetChildren()) do
                 if gui.ClassName == 'BillboardGui' then
                        gui.Enabled = true
                  end
            end
        end
    end 
end


mouse.KeyDown:connect(onKeyDown)