How to create a premium modal gui?

Hello, i'm trying to make a GUI where players can buy Premium. I tried a script i found for a teleport and remaked it for a gui but didn't worked.

Here is the script:

local MarketplaceService = game:GetService("MarketplaceService")
local Players = game:GetService("Players")

local showPrompt = true

script.Parent.MouseButton1Down:Connect(function()
	local player = Players.LocalPlayer
	
	if player.MembershipType == Enum.MembershipType.Premium then
		script.Parent.Parent.Parent.Parent.Visible=false
		script.Parent.Parent.Parent.Parent.Parent.PremiumError.Frame.Visible=true
		wait(3)
		script.Parent.Parent.Parent.Parent.Parent.PremiumError.Frame.Visible=false
		script.Parent.Parent.Parent.Parent.Visible=true
	else
		if showPrompt == false then return end
		showPrompt = false
		delay(5, function()
		showPrompt = true	
		end)
		MarketplaceService:PromptPremiumPurchase(player)
		warn("Prompted Premium purchase")
	end
	MarketplaceService.PromptPremiumPurchaseFinished:Connect(function(player)
	warn("Premium modal closed")
end)
Players.PlayerMembershipChanged:Connect(function(player)
	warn("Player membership changed; new membership is " .. tostring(player.MembershipType))
	if player.MembershipType == Enum.MembershipType.Premium then
		script.Parent.Parent.Parent.Parent.Visible=false
		script.Parent.Parent.Parent.Parent.Parent.PremiumUpdate.Frame.Visible=true
		wait(3)
		script.Parent.Parent.Parent.Parent.Parent.PremiumUpdate.Frame.Visible=false
		script.Parent.Parent.Parent.Parent.Visible=true
	end
end)
end)

Thanks for the help already!