The GTIN you send to us might not exist in our database yet. We are constantly enriching our existing and future data with GTIN. Nevertheless, it will be impossible to have all existing GTIN for a product or even one GTIN for every product in our product catalogue (strongly dependent on category). If you are in possession of original manufacturer GTIN for the products you sell please reach out to listing@refurbed.com so that we can add them to our database and you have an easier time mapping your products.