Adding UPCs, EANs, and ISBNs for Your Products
Most categories require sellers to use a product identifier to create new product pages and offer listings on the Amazon.com website. The most common identifier used by sellers is a UPC.
If you don’t provide a UPC, EAN, or ISBN, you will generally receive an error message. When this occurs, you will need to add the product’s identifier in order to create a new product detail page in the Amazon.com catalog or complete your inventory offering. (If you don’t have a UPC, EAN, or ISBN for your product, see How to Obtain a Product Code.)
The UPC field is supported in the Add a Product tool and in Inventory File templates.
Add a Product
The Add a Product tool will allow you to create new product detail pages and offerings one at a time. If you search for a product and find it in our catalog, the UPC, EAN, or ISBN will be automatically entered for you and you can continue to create your offering. If you create a new product detail page, you can enter the UPC or EAN on the “Add This Product to Our Catalog” page after completing the product classification step.
From Amazon Seller Central