This article explains how to synchronize your shipment information with FedEx and print the specific labels for that carrier.
To keep in mind:
FedEx allows to send up to 150 pounds (68.0389 Kg) per line.
The maximum number o boxes per line that FedEx allows to ship is 40 boxes.
Instructions
Failed Processes
When the process fails for any reason, hover the mouse over the warning icon next to FedEx name from the Order Summary screen. You will see the reason why the information could not be sent to FedEx. Click on the Resend FedEx Details button to retry once you have checked the issues.