Telnet login RHEL 8 host by AD users getting permission denied

Issue

• RHEL 8 server telnet-server.example.com is a telnet server which integrates directly to AD domain example.com
• When trying to telnet in this host with an AD user aduser@example.com, getting Permission denied, and the session closes, but telnet root@telnet-server.example.com does work.

[root@telnet-server ~]# telnet localhost
Trying ::1...
Connected to localhost.
Escape character is '^]'.

Kernel 4.18.0-348.12.2.el8_5.x86_64 on an x86_64
telnet-server login: aduser@example.com
Password: 

Permission denied
Connection closed by foreign host.