European Article Number it is a # barcode' . It's to identify specific products.
If N/A does not work or leasving it blank does not work, then call eBay Customer Support from the Help & Contact tab above ask what they suggest. Lines open between 8 a.m. to 10 p.m.
If these are all new items, you need to register as a business on eBay, it does not matter the volume sold, or the price fetched, it's the fact the items are all new. That may take you out of the dilemma.
