Got an error called "Attempt to index nil with 'leaderstats'." How can I fix this?

I am writing a script where if you press a button a certain amount of time, a closed barrier will open.

This is the script I wrote:

game.Players.PlayerAdded:Connect(function(plr)
	local leaderstats = Instance.new("Folder")
	leaderstats.Parent = plr
	leaderstats.Name = "leaderstats"
	
	local Points = Instance.new("IntValue", leaderstats)
	Points.Name = "Points" -- Code for the leaderstat.
end) 

local clickDetector = game.Workspace.Button.ClickDetector

clickDetector.MouseClick:Connect(function(plr) 
	plr.leaderstats.Points.Value = plr.leaderstats.Points.Value + 1  -- Adds a point every time the player clicks the button.
end) 

if plr.leaderstats.Points.Value >= 30 then
	game.Workspace.Barrier.BrickColor = BrickColor.new("Lime green")
	game.Workspace.Barrier.CanCollide = false
end -- I want this to run if the players' points are greater than or equal to 30, only gave me an error.

I put the code above inside a normal script at ServerScriptService. Whenever I playtest the game this error appears: 16:16:57.032 - ServerScriptService.Leaderstats:16: attempt to index nil with 'leaderstats'. I was expecting that the barrier will open once the player has 30+ points...

The code runs perfectly fine and adds one point every time I click the button... until it reaches line 16. The error told me that there's something wrong with it. I do not know what part of it I did a mistake or if I used a wrong syntax.

I tried doing this and this one, doesn't work or am I missing something?

First, the plr argument can only be used in the function, place all the codes inside the PlayerAdded function and it would fix the error. Secondly, the if statement will only be checked once, use :GetPropertyChangedSignal() or .Changed to fire a function and check if the value reaches 30 or higher. The code should be like this.

game.Players.PlayerAdded:Connect(function(plr)
	local leaderstats = Instance.new("Folder")
	leaderstats.Parent = plr
	leaderstats.Name = "leaderstats"
	
	local Points = Instance.new("IntValue", leaderstats)
	Points.Name = "Points"
	
	local clickDetector = game.Workspace.Button.ClickDetector
	
	clickDetector.MouseClick:Connect(function(plr) 
		plr.leaderstats.Points.Value = plr.leaderstats.Points.Value + 1
	end) 
	
	plr.leaderstats.Points.Value:GetPropertyChangedSignal("Value"):Connect(function()
		if plr.leaderstats.Points.Value >= 30 then
			game.Workspace.Barrier.BrickColor = BrickColor.new("Lime green")
			game.Workspace.Barrier.CanCollide = false
		end
	end)
end)