FedEX - Authentication failed error

On despatching live orders with FedEx for the first time you may encounter the following error:

The first thing to check is that you've swapped your 'test credentials' on the integration for your 'production credentials' which will have been provided to you by FedEx. Please also check with StoreFeeder support if your account has been swapped back to use production credentials which are required for live despatch.

If the error still persists we'd recommend contacting FedEx to double check you've got the correct credentials and everything has been enabled on their end.