DevProductButton

--don't blame me if it has an error because of where you've placed it
local MarketplaceService = game:GetService("MarketplaceService")
local Players = game:GetService("Players")

local productID = 000000000

local button = script.Parent

button.MouseButton1Down:Connect(function()
    local player = Players.LocalPlayer
    MarketplaceService:PromptProductPurchase(player, productID)
end)