Argument 1 missing or nil?

robu = game.Players.Player:GetFullName()

while true do
	script.Parent.Text = "Robux Ammount: "..game.Players:FindFirstChild().leaderstats.ROBUX
wait()
end

why does it not work? it's soppost to make the textbutton display the ammount of robux the player has.

You didn't use robu at all? Anyways;

local player=game.Players.LocalPlayer

while true do
	script.Parent.Text="ROBUX Amount: "..player:FindFirstChild("leaderstats").ROBUX
	wait()
end

Even better thing to do would be;

local player=game.Players.LocalPlayer
local robux=player:FindFirstChild("leaderstats").ROBUX

robux.Changed:connect(function(val)
	script.Parent.Text="ROBUX Amount: "..val
end)