The entry of an EAN / UPC number when listing to eBay is now mandatory for certain categories. This is a recent change made by eBay themselves (see the following link).
eBay Seller Release: Product identifiers
OpenBay Pro allows entry of the EAN / UPC number on the 'Features' tab - but currently only in our BETA versions. You can update to the OpenBay Pro BETA version from your OpenBay Pro dashboard - please see the following link.
If you have any difficulties updating your module, we do offer a paid service - please raise a support ticket if you require more information (link below).