AuthService.svc doesn't throw an error when login on UI does

Hi support team :)  

I just found out that when I can't login on UI because of the Error

  I still can login via authentication service by doing Post request and receive all the cookies needed (like it is described here https://academy.creatio.com/documents/technic-sdk/7-16/executing-odata-…). And only when I perform second request as so called  "logged in user" I am interrupted with the the Error:

licManagerException.message = 'Unable to log in: insufficient number of licenses to access the objects used on the portal. A system administrator can modify the list of objects available to portal users';

Thus I do wonder why I am not receiving  'Unable to log in..' error message when I do authentication Post request ? I must be receiving this error message no matter how I am logging in.

Thank you

Looking forward to your reply