250002: Invalid Authentication Information
If, for some reason, the plugin cannot establish the connection with the UPS API, you will see the error message coming from the API with the detailed information on the cause of the problem, e.g.: 250002, 250003
To resolve 250002: Invalid Authentication Information connection problems, please consider switching to the Client Credentials feature. If you continue to see the same error despite switching to Client Credentials, then please follow these steps:
Step 1: Enter the application you created and hit the ‘Edit App’ button developer.ups.com/apps 
Step 2:Add ‘Authorization (OAuth)’ ‘Rating’, ‘Address Validation’, ‘Locator’ applications using the plus button 
Step 3:Select ‘Authorization Type: Client credentials’ and hit ‘Save changes’ button 