My script says it's working, but doesn't make the GUI I chose visible?

I'm trying to make a simple chat command, a whitelisted player will be able to say "gui" and the GUI I chose should become visible. It will also say a message in console "GUI Script Working!" but it doesn't show the GUI, it only says the text in the console, does anyone know why this is happening? (I'm new to scripting sorry for the lack of knowledge.)

local isAdmin = {["Tantalingo"] = true} -- "Tantalingo" is my username
 
function findPlayer(name)
    for _, player in ipairs(game.Players:GetPlayers()) do
        if player.Name:lower() == name:lower() then
            return player
        end
    end
end
 
function onChatted(message, player)
    if message:sub(1, 5) == "gui" and isAdmin[player.Name] then
       game.StarterGui.AccessUI.Main.Visible = true
		print "GUI Script Working!"
        end
    end
 
game.Players.PlayerAdded:connect(function(player)
    player.Chatted:connect(function(message) onChatted(message, player) end)
end)

It is because you are changing StarterGui which is where GUI is stored and copied into a players PlayerGui when they join or respawn. To access a players gui you must be in a LocalScript and use:

game.Players.LocalPlayer.PlayerGui