I know you can use this for anything in the catalog..
local Asset = game:GetService("MarketplaceService"):GetProductInfo(0000000)
But Developer Products aren't in the catalog.. They are only connected to the game and no one other then the owner can see the product.
You have to give GetProductInfo a second optional parameter.
local Product = game:GetService("MarketplaceService"):GetProductInfo(developerProductId, Enum.InfoType.Product)