After a Jet.com store is connected to ShipStation, you will have access to the Jet Listing fields for your product records as well as a CSV file template to import/update the fields in bulk.
To access this in ShipStation, go to the Products tab, click Import, then select Download Sample CSV file.
When bulk importing the Jet Category into ShipStation, you must enter the numerical Node ID that corresponds to the Jet Listing Category into the CSV. Here is the complete list of available numerical Node Ids and the Jet Listing Category mapping.
You can upload either an L0, L1, or L2 node ID. For example (using the first line of categories from the downloaded spreadsheet) you could upload ID 1000000 into ShipStation, and Jet would add that to their Books & Other Media category.