Barcode (ISBN, UPC, GTIN, etc.)
Barcodes are typically used by resellers. The identifier needs to be a new or existing Global Trade Item Number (GTIN). Some sales channels require a GTIN before a product can be published using the channel.
GTINs are unique identifiers used internationally to store and locate product information. UPC, EAN, and ISBN numbers are examples of GTINs, which might vary in length depending on the product type. You can find the GTIN above or below the barcode on the packaging for your product.
If you don't have a GTIN for a product, then you can request it from the manufacturer. Don't invent false GTIN information for your products.