Required if the referenceType field is included in the request. This is the identifier of an object of the type specified by the value of referenceType. For example, if the value of referenceType is INVENTORY_ITEM, this field should contain the seller's SKU for an inventory item.
The type of object that the requested change is intended to support. This applies to objects that are incomplete due to the need for a matching catalog product. Providing a referenceType and a referenceId in a catalog change request enables eBay to automatically apply the resulting new or updated product directly to the specified object without requiring additional action on your part.
INVENTORY_ITEM — The requested change will support the completion of an inventory item, which you can then use to create an offer.
LISTING — The requested change will support the modification of an active product listing.
LISTING_DRAFT — The requested change will support the completion of an offer, which you can then publish as a product listing.