This endpoint is perhaps the most important for App Developers. If the Shipping Method for a Shipment is vendor_shipping: false, Sellers are required to provide valid tracking information in order to receive a payout for their Shipment/Order. During the fulfillment process, once a shipment has been physically shipped or the known tracking information for a shipment has been generated, use this endpoint to send TSL the carrier_id and tracking_number for the shipment using the shipment.id. Carrier Ids can be obtained from the /carriers/ endpoint. Please note that TSL currently supports US-only shipments.