You can upload your tracking numbers within the Customer → Fulfillment page by using the Import Tracking button:

The upload will require you to import a CSV file. This can be in the same format as the file downloaded from the Fulfillment Search page. You can accomplish this by downloading the file using the Export CSV button, adding the tracking numbers to the designated column (Z), and then uploading the modified file after removing any rows above the column headers.

Fulfillment records must be in a HOLD status prior to importing the file containing the tracking numbers.

Alternatively, you can construct your own CSV file, using the following fields:

Sample file which can be used to build your CSV: