Sellers use this call to provide new or verify existing tracking information for one package being shipped to the buyer. When a case involves multiple quantities of an item, hence multiple packages, this call must be made by the seller for each package being shipped to the buyer.
This optional field allows the seller to add a comment intended to be read by the buyer receiving the tracking information. For example, the seller might add a comment such as this in the field: "Here is the shipment tracking number that you requested."
The shipment tracking number. eBay checks to verify that the tracking number is consistent with the numbering scheme used by the specified shipping carrier, but eBay cannot verify that the tracking number is accurate. Accuracy is the responsibility of the seller.
See the Field Index to learn which calls use trackingNumber.