Error 21919301: UPC / EAN is missing
eBay MPN / UPC / EAN / ISBN Requirements
eBay uses an item’s brand, manufacturer part number (MPN), and global trade item numbers (GTINs) — such as Universal Product Codes (UPC), European Article Codes (EAN) and International Standard Book Numbers (ISBN) — to help buyers quickly find the items they’re looking for. For sellers, including these product identifiers not only increases your items’ visibility in eBay search results and navigation, it improves your placement in search engines like Google and Bing, too. To take full advantage of these benefits now, include product identifiers every time you list.
eBay Categories That Require Product Identifiers
http://pages.ebay.com/sellerinformation/news/springupdate2015/product-identifiers.html#FAQ1-10
eBay's Product Identifier Requirements & WP-Lister
With eBay's new requirements for product identifiers, listings that used to list properly may now result in the following error or similar for other product identifiers:
Error: Required field, UPC, is missing. (21919301) or
Error: Required field, EAN, is missing. (21919301)
If you have a product identifier for your product, you can simply add in the product identifier under Advanced eBay Options in the edit product page.
Adding Product Identifiers to Variations
Starting September of 2015, eBay will require Product Identifiers for each variation of a multi-variation listing. To add a product identifier to a variation, simply visit the variation and enter the UPC/EAN/MPN/ISBN in the available fields.
Please note that the MPN and ISBN fields are disabled by default to reduce clutter. If your variations or simple products have MPNs or ISBNs, you have to enable these fields on the advanced settings page first in order for the MPN and ISBN fields to appear in the edit product page.
What Do I Do if I Don't Have a Product Identifier?
If you don't have a product identifier for your product(s), eBay will allow you to enter "Does not apply" (for english eBay sites) instead of an EAN/UPC code. This change can be achieved by updating to version 2.0.9.5, a new setting is available that adds an option labeled "Missing Product Identifiers" on the eBay > Settings > Advanced page where you can tell WP-Lister to fill in missing UPCs or EANs with "Does not apply" automatically.
For more information on eBay's new requirements check out this seller news page:
http://pages.ebay.com/sellerinformation/news/springupdate2015/product-identifiers.html