This table explains the data between eBayLINK and WooCommerce
eBay LINK, WooCommerce, and Marketplace data mapping
SKU
This is the WooCommerce product ID - a number generated by WooCommerce when you create a product.
Retailer Reference
This is the WooCommerce Variant ID - a number generated by WooCommerce when you create a product.
MPN
WooCommerce Data: This is the Variant SKU from WooCommerce.
Marketplace Data: MPN Field in Marketplace.
UPC / EAN / ISBN
WooCommerce Data: This can be set up as a custom attribute of the product. The name of the attribute must be one of UPC, EAN or ISBN, as appropriate in WooCommerce. See FAQ UPCs, EANs in WooCommerce.
Marketplace Data: UPC field in Marketplace.