Some categories may require item specifics, or they may require you to use eBay's predefined names or values, rather than using your own. For example, clothing categories typically require you to specify Brand and Color as item specifics. (Color can optionally be specified in variation specifics instead. Refer to Multiple-variation Listings for additional information.)
To determine which item specifics are required for a leaf category, call the getItemAspectsForCategory method of the Taxonomy API. For each aspect included in the response, if the value of the associated aspects.aspectConstraint.aspectRequired field is true, that aspect is required.
Note that in some categories, item specifics may not be required, but it is always best practice to use recommended item specifics if they are relevant to your item.