What's wrong here?

This is a pretty simple script.. but doesn't work.. Why??

What it should do is delete a ScreenGui (script.Parent.Parent) fro the player's (game.Players.LocalPlayer) StarterGui....

if GamePassBlock == true then 
    if game:GetService("GamePassService"):PlayerHasPass(player, GPID) then
    script.Parent.Parent:Destroy()
    end
end

Could it be that ("GamePassService"):PlayerHasPass will only work in server scripts?