How would I decline a developer product purchase?

I am creating a song purchasing system and I want to decline the developer product if the sound ID is not correct so how would I return something that would not allow the purchase to go through.

What you can do is check to see if the Id is correct using the method GetProductInfo of MarketplaceService before initiating the purchase:

local m = game:GetService('MarketPlaceService')
local id = 0

if m:GetProductInfo(id).AssetType == 3 then -- if id is associated with a sound
    -- initiate purchase
end

An example ^