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 
Invalid Access License number (250003)
The error message “Invalid Access License number (250003)” typically indicates an issue with the UPS Access License number that you’ve entered in the plugin settings.
Please double-check the UPS Access License number in your plugin settings to ensure it’s entered correctly without any typos or extra spaces. This number should match exactly with the one provided by UPS when you registered for an API key.
If you’ve verified that the Access License number is correct and the issue persists, it may be necessary to regenerate a new Access License number from the UPS Developer Kit page and update the plugin settings with the new number.