This string value is the unique identifier of an eBay category. In GetItem and related calls, see the CategoryName field for the text name of the category. The parent category of this eBay category is only shown in GetCategories.
In an Add call, the PrimaryCategory.CategoryID is conditionally required unless the seller successfully uses the ProductListingDetails container to find an eBay catalog product match. When the seller successfully uses an eBay catalog product to create a listing, the listing title, listing description, item specifics, listing category, and stock photo defined in the catalog product is used to create the listing.
In an Add/Revise/Relist call, the SecondaryCategory.CategoryID is conditionally required if a Secondary Category is used. Using a Secondary Category can incur a listing fee.
For ReviseItem only: Previously, removing the listing from a secondary category was only possible within 12 hours of the listing's scheduled end time when an auction listing had no active bids or a multiple-quantity, fixed-price listing had no items sold, but this restriction no longer exists. Now, the secondary category can be dropped for any active listing at any time, regardless of whether an auction listing has bids or a fixed-price listing has sales. To drop a secondary category, the seller passes in a value of
0 in the SecondaryCategory.CategoryID field.
See the Field Index
to learn which calls use CategoryID.