Pre-fills the tracking of the sales order’s next shipment. When a fulfillment is created without its own tracking, this value moves onto that fulfillment and is cleared from the sales order. A sales order can ship in several fulfillments, each with its own tracking, so after shipping read and set tracking on /sales_order_fulfillments. If the sales order already has fulfillments, the value is written to all of them, so on a partially delivered sales order it overwrites the tracking of the earlier shipments. A fully delivered sales order with more than one fulfillment returns 422. To set the tracking of one shipment, use PATCH /sales_order_fulfillments/{id}.
