Why does this give free items??

I have a code that I want players to BUY the cash, instead, the Purchase Panel pops up, and gives the cash without even buying it... I need help here!

-- Yep, it's in a LocalScript, in case anyone asks
buybutton = script.Parent
msp = game:GetService("MarketplaceService")
id = 19251916
p = game.Players.LocalPlayer
buybutton.MouseButton1Click:connect(function ()
	msp:PromptPruductPurchase(p,id)
	p.leaderstats.Diamonds = p.leaderstats.Diamonds + 1000
end)

Its because its coded so when the gui pops up, the cash is given

buybutton = script.Parent
msp = game:GetService("MarketplaceService")
id = 19251916
p = game.Players.LocalPlaye
buybutton.MouseButton1Click:connect(function ()
    msp:PromptPruductPurchase(p,id)
end)

I think developer products are scripted in a seperate script than the one that prompts the purchase