We got a call from eBay stating that MPN is required on our listings from 29th June - do I provide this via ProductListingDetails - BrandMPN - MPN or via Item Specifics? We were listing via UPC so when I added the MPN into ProductListingDetails it seems to get ignored (presume because first match is UPC?) Is there any value in specifying both UPC and MPN in ProductListingDetails section? If in Item Specifics can I always just add "MPN" or does it vary from category to category? We have near 20,000 items listed so it's spread across a lot of categories! Thanks.