The item-specific Brand is missing

For each of the eBay categories, there are mandatory product specifics that must be filled out for the product to be correctly listed on the Channel.

With M2E Sales Channels, you can easily manage the specifics via eBay Configuration. Find the gear icon in the upper left corner of the eBay listings page to open eBay Configuration. 

Move to the Categories tab and find the Total/Used Specific column. Click Set for each category that has this button to specify all required specifics for the listing category. Use a Custom Value or an External Attribute (Shopify Metafield/BigCommerce Custom Field/WooCommerce Attribute) to set up the required specifics properly.

You also can manage specifics for each listed product separately. To do this, find a product for which you want to set or change the Specifics. Open the product details card to find the Specifics section on the General tab. 

Once you complete the setup, please confirm your changes, and updates will be sent to eBay automatically.