Currently, for International shipments, the ITN number does not appear anywhere on the FedEx auto-generated Commercial Invoice (Customs Form). Please have the ITN number show up on the FedEx Commercial Invoice.
Thank you for your post. I have spoken with the developers, and they would like you to submit a ticket to support@shipstation so they can email you back and forth with some additional questions about your request to " put ITN number on FedEx Commercial Invoice (Customs Form)."