A 401 Transfer Error indicates that the request failed due to missing or invalid authentication credentials. This error is triggered due to unauthorized access or restricted permissions. When a "Transfer Failed: Request failed with status code 401" error occurs, it suggests that the username, password, or account code supplied for the transfer is incorrect. The server or service you are trying to reach expects you to log in or present valid credentials (e.g., a token, API key, or username/password), but it has not received them—or the credentials provided are invalid or expired. You can typically resolve a 401 error.

To resolve a 401 Transfer Error, consider the following steps:

Verify Credentials: Start by double-checking the username, password, and account code being used for the transfer. Ensure they are correct and that there are no typos. Also, verify the account code or suppression list ID. Verify that your authentication process matches the requirements of the server and ensure that your credentials are correct and up to date. 

Test Login: Paste the username and password directly into the login page to ensure they work. If the login fails, the credentials are incorrect.

Check API: If you are accessing a third-party API or resource, confirm the exact authentication mechanism they require.

Check Server Logs: The logs will often provide more detail about why your credentials were disallowed.

Contact Support: Reach out to your third-party API or resource to double-check the login and password and verify that the API endpoint or file server is accessible to the account or client you’re using.

Other potential solutions:

1. Look for errors in the URL.
2. Clear your browser's cache.
3. Flush your DNS.
4. Deactivate your WordPress plugins.
5. Check the WWW-Authenticate header response.

*Please note - If you are unable to resolve the 401 Error and you need assistance with this, please contact us: support@optizmo.com