FedEx Error when generating a Shipping Label : ERROR:  Authentication Failed
There are two things that we need to check on this error:
1. Your credentials are incorrect. If you copy-pasted them from an email or similar, make sure there are no additional spaces before or after.
2. You need to become certified to generate the FedEx production shipping label. See below:
See: Complete the Label Certification Process
Interprise Suite 6 and Connected Business and up