When using Amazon you will need to have a UPC code. A UPC code is a bar code used for tracking your product. These codes are created by a company called GS1. You can buy them online. One place to look would be barcodemania.com where you can buy in bulk or buy one at a time.
When selling on Amazon you will need a UPC code (Item Number) for every product you sell. Each variation of that product will need a code. So if you have several colors and sizes they will all need a separate code.
If you have any other questions on UPC codes please let us know. You can email firstname.lastname@example.org