Why does my script only work in solo testing?

I made this script and it works perfect in solo testing but it doesn't work in normal game.

while true do
    game.Players.LocalPlayer.leaderstats.Score.Value = game.Players.LocalPlayer.leaderstats.Score.Value + 1
	local str = game.Players.LocalPlayer.leaderstats.Score.Value
	local str1 = "Your income: "
	game.Players.LocalPlayer.PlayerGui.ScreenGui.Frame.TextButton.Text = str1..str
	wait(1)	
end

The most common cause for a LocalScript to malfunction in a sever environment is an attempt to access something that is instantiated very quickly when run locally, but more slowly on a server, for example ... the Player!

All you need to do is add a loop that waits until the player, and in some cases the specific thing that you want, exist:

while not game.Players.LocalPlayer do wait() end
player = game.Players.LocalPlayer

while not player:FindFirstChild("leaderstats") do wait() end
stats = player.leaderstats

while true do
    stats.Score.Value = stats.Score.Value + 1
    local str = stats.Score.Value
    local str1 = "Your income: "
    player.PlayerGui.ScreenGui.Frame.TextButton.Text = str1..str
    wait(1) 
end