If you have the “prof 1000 authentication failed” problem when trying to use FedEx, it may be because by that your FedEx is still in test mode in your account.
 
To use FedEx as your shipping method you may follow steps below.
Step 1:Navigate to "Shipping"->"FedEx".
Edit the FedEx information and input your account information with it in test mode. This is for you to test your FedEx account.
Step 2: Contact FedEx.
Generally FedEx will send you a confirmation email with new account info (key, account ID etc.). Input your new FedEx info in Miiduu store settings and change the Test Mode to No.