Thank you for using FedEx Online Support. I apologize, but not all references will appear on invoices. All references except 'Invoice no.' print on the FedEx Express, FedEx Ground, and FedEx Express Freight invoices. If your customer is using the “Invoice No” field, they would be better service to move that information to another field. In other words, the 'Your reference,' ‘P.O. no,’ and the ‘Department no’ fields shopuld be printing on their invoices.