How to access CoreGui from a local script?

So I'm trying to create an anti-cheat script I saw in a game. It would detect if there is a new undetected GUI for a player (e.g a remotespy GUI) so it will ban it. However, whenever I write game.CoreGui, it will just say The current identity (2) cannot Class security check (lacking permission 1). The localscript is in StarterCharacterScripts. I got 2 actually, one has this:

local plr = game.Players.LocalPlayer
game.DescendantAdded:Connect(function(d) 
    if (d.Parent==game.CoreGui) then
        if (d.Name == "SpyScroller") then
            local http = game:GetService("HttpService")
    local Data = {
        ["content"] = plr.Name .. " used a cheat. Cheat: Not game-source local GUI! Probably using remote spy. Banned for 1 week!"
    }

    Data = http:JSONEncode(Data)
    http:PostAsync("mydiscordwebhooklink", Data) --Put the link you saved between the two quotes.
    plr:Kick("You have been banned for using cheats! Duration: 1 week! Appeal in our discord server, #banappeals")
        end
    end
end)

and one has this:

local safeguinames = {"admingui"}
local normalamount = 4 --Don't edit this.
local plr = game.Players.LocalPlayer
while wait() do
    if (#plr.PlayerGui:GetChildren() >= #safeguinames) then
        --check if it's admingui
        if (#plr.PlayerGui:GetChildren() == 5 and plr.PlayerGui:FindFirstChild("admingui")==false) then
            --ban.
            local http = game:GetService("HttpService")
            local Data = {
                ["content"] = plr.Name .. " used a cheat. Cheat: Not game-source local GUI! Probably using remote spy. Banned for 1 week!"
            }

            Data = http:JSONEncode(Data)

            http:PostAsync("discordhook", Data) --Put the link you saved between the two quotes.
            plr:Kick("You have been banned for using cheats! Duration: 1 week! Appeal in our discord server, #banappeals")
        end

        if (#game.CoreGui:GetChildren()==8) then -- I think this part is not needed if I have that first script, but it still gives the same error
            local http = game:GetService("HttpService")
            local Data = {
                ["content"] = plr.Name .. " used a cheat. Cheat: Not game-source local GUI! Probably using remote spy. Banned for 1 week!"
            }

            Data = http:JSONEncode(Data)

            http:PostAsync("stillmydiscordhook", Data) --Put the link you saved between the two quotes.
            plr:Kick("You have been banned for using cheats! Duration: 1 week! Appeal in our discord server, #banappeals")
        end
    end
end
--And I know it won't ban, this is just testing..

EDIT: Don't care about the dumb script I have many things to do with it but I want to solve this problem first. So what should I do?