AD error after update .net core

In an app I have installed on prod, error is thrown when try to login with AD security:

System.NullReferenceException: Object reference not set to an instance of an object.
at ReeConf.Authentication.ApplicationUserManager.get_Domain() in C:\Labs\Radzen\REEConf\server\Authentication\ApplicationUserManager.cs:line 50
at ReeConf.Authentication.ApplicationUserManager.FindByNameAsync(String userName) in C:\Labs\Radzen\REEConf\server\Authentication\ApplicationUserManager.cs:line 95
at ReeConf.Controllers.AuthController.d__8.MoveNext() in C:\Labs\Radzen\REEConf\server\Controllers\AuthController.cs:line 106
--- End of stack trace from previous location where exception was thrown ---

Could you guide me about how to correct this issue?

Thanks

The source code of the Domain property is like this:

private string Domain
{
    get
    {
       return options.User.Split('@').Last();
    }
}

Getting NullReferenceException would mean that either options or User is null. Is the user name set in the Active Directory security settings in Radzen?

Where in security settings is this settings?

It is the last option in your screenshot. Did you add any custom code? We tried to reproduce the issue but everything seems to work successfully. Can you log in development? You can check the appsettings.json file on your server and in development to see if there are any errors.

Fixed. An invalid char in appsettings.json was the cause. Thanks!!!