Why won't this work?

Hey all. I need help with selling a developer product through a GUI, that also awards a gravity coil. (that lasts one life, but that doesn't matter). I think I have the award gravity coil thing down, but the GUI doesn't work and isn't popping up the developer product thing. This is the whole script in TextButton.

local plr = script.Parent.Parent.Parent

local function buyItem(button)
    button.MouseButton1Click:connect(function()
        local marketId = button["market"].Value
        link:PromptProductPurchase(plr,20282186) 
        link.ProcessReceipt = function(receiptInfo)
            if Enum.ProductPurchaseDecision.PurchaseGranted and receiptInfo.PlayerId == plr.userId then
                game.Lighting.GravityCoil:Clone().Parent = plr.Backpack
            end
        end
    end)
end

Thanks for the help!