What is 401 unauthorized access is denied due to invalid credentials?

Error 401: Unauthorized: Access is denied due to invalid credentials. Error 401 occurs when trying to access Administrative and Help-Desk Portals, while Self-Service Portal works fine. This error is returned by Internet Information Services (IIS). It occurs when the authentication to Admin or Helpdesk portal fails.

For More Information Please Refer: https://kb.netwrix.com/1162