Gui appears in studio but not the actual game?

local player = script.Parent.Parent
local playerGui = player:FindFirstChild("PlayerGui")

if not playerGui:FindFirstChild("mainMenuCopy") then
	local menuGui = game.ServerStorage.mainMenu:clone()
	menuGui.Parent = playerGui
	menuGui.Name = "mainMenuCopy"
end

this is the script that makes the menu appear when you first join the game, but it only appears in studio when I test it in studio. Thanks in advance :D

EDit: This script is placed in starterPlayerScripts