How do I make a Developer product GUI?

Can anyone tell me how to make a GUI that you can buy Developer Products from?

I do this sort of thing all the time. This script is what I put inside of a GUI button. Here's the code I use:

script.Parent.MouseButton1Click:connect(function()
	id = 123456 -- This is a random ID, be sure to replace this with the Developer Product's actual id
	service = game:GetService("MarketplaceService")
	service:PromptProductPurchase(player, id)
end)

service.ProcessReceipt = function(receiptInfo)
	if receiptInfo.ProductId == id then
		-- Whatever the developer product does, put that here
	end
end

Keep in mind that you need to set the variable "player" before using PromptProductPurchase().