Vendors are required to ship items and transmit a valid shipment tracking number that shows movement within 2 business days from the date the orders went to PO (the day you received the order file).
You can upload tracking by CSV file in the admin portal or through API/ShipStation integration.
To upload tracking in the portal:
Log in to https://admin.untilgone.com
Click Fulfillments > Tracking Upload
There are instructions at the top of the screen.