Enable SKU (Custom Label) field on eBay
eBay is very peculiar in the sense that one of the most basic information for a product - namely SKU is not readily visible or available.
eBay uses a field named "Custom Label" as the product SKU. It is highly recommended to set SKU (Custom Label) for eBay listings, to make it easier to integrate with QuickBooks or any other system to identify products sold, and to update Inventory to eBay.
Follow these steps to make the Custom Label field visible and editable on your eBay account.
Step 1: On your eBay account, click on My eBay > Activity > Selling Manager Pro
Step 2: Click on Active to all your active listings
Step 3: Find the Custom Label field on each listing
Step 4: Now click on the Add to assign Unique SKU to your listing on eBay