Data Persistence Not Working

I am working on an intro script for a friend and I am trying to make it play only the first time you join. I looked up how Data Persistence works and found that you can use some methods to make it easier. I have done this exactly the way the tutorial suggested, and it hasn't worked.

game.Players.PlayerAdded:connect(function(player)
	player:WaitForDataReady()
	local joined = player:LoadString("AlreadyCome")
	if joined == nil then
	--DoIntroStuff

At the end of the script I have got

player:SaveString("AlreadyCome", "I'veBeenBefore")
	player.PlayerGui.NewGui.Exit.MouseButton1Down:connect(function(mouse)
	player.PlayerGui.NewGui:remove()

After looking at it through test mode, I can see that Boolean value 'DataReady' doesn't turn to true. Please help.

Here's another idea how bout you put the intro in the ServerStorage then do this

game.Players.PlayerAdded:connect(function(p)
Intro = game.ServerStorage["Intro Name"]:Clone()
Intro.Parent = p.PlayerGui
end)

This was done on an IPad sorry if has simple errors

For only one time join do this

game.Players.PlayerAdded:connect(function(p)

Local bintro = Instance.new("BoolValue", p)
bintro.Name = "Intro"

p:WaitForDataReady()

p:LoadBool("intro") -- not sure if it is bool or Boolean

if p.Intro.Value == false then
Intro = game.ServerStorage["Intro Name"]:Clone()
Intro.Parent = p.PlayerGui
end
end)

game.Players.PlayerRemoving:connect(function(p) p:SaveBool("intro", p.Intro.Value) end)