For many product categories, eBay requires sellers to include product identifiers. The identifiers are:
Read more about product identifier requirements here.
The UPC set on the product home page will be sent to eBay when listing the product. If the item does not have a UPC a value of "Does Not Apply" will be sent, which is also valid for eBay. eBay will then place the UPC into the item specifics on the eBay listing.
Sending Product Identifiers
The Brand and Manufacturer SKU (MPN) should be set as item specifics on the eBay properties page when listing the item, in order to satisfy eBay's requirements. Even if those values have been set on the product home page they will not be mapped, by default, to the item specifics on the eBay properties page. However, you can use the eBay Global Item Specs page to map those fields and send them as items specifics.
To update products that are already listed, use the action Revise All Listings on the eBay Properties page. If the product identifiers are set as items specifics, you can use the action Revise Items Specifics. These action can be done to bulk update the product from the manage inventory page when in eBay Mode.