with this script a GUI should appear after a dev product has been bought ?

why does my script dont work ?

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

local productID = 1069575853

local function processReceipt(receiptInfo)
		
	local player = players:GetPlayerByUserId(receiptInfo.PlayerID)
	if not player then
		return Enum.ProductPurchaseDecision.NotProcessedYet
	end

	if player then
		local PlayerGUI = player.PlayerGui
		local BalloonGui = game.ReplicatedStorage.GUI.DevProducts.BalloonGUI
		BalloonGui.Parent = PlayerGUI
	end

	return Enum.ProductPurchaseDecision.PurchaseGranted

end

MarketplaceService.ProcessReceipt = processReceipt()