Hello Prasenjit
The radius-server host command has been deprecated in newer devices and OSes and it has been replaced with the following syntax:
radius server MY_SERVER
address ipv4 192.168.1.101 auth-port 1812 acct-port 1646
key radiuspass
Take a look at this Cisco command reference for more details:
I will let @ReneMolenaar know to consider updating the lesson.
I hope this has been helpful!
Laz