FreeRadius PAP Authentication Issue : WARNING: Unprintable characters in the password. Double-check the shared secret on the server and the NAS! Using Post-Auth-Type Reject ().[pap] Passwords don't match

If you are seeing this in radius log

WARNING: Unprintable characters in the password.  Double-check the shared secret on the server and the NAS! Using Post-Auth-Type Reject ([pap] Passwords don't match).

 [pap] login attempt with password "5?q¦¦?!##+Y?E¦¦"
[pap] Using clear text password "mypassword"

Do nothing until this warning is disappeared. To troubleshoot this use following

1) Match your key as described in warning .(NAS shared secret and shared secret on other Service like VPN in my case )

2) If keys are same and still FreeRadius is NOT Authenticating then change your secret to some simple secret like ("mysecret"). This may be due to too long shared secret or data type conversion mismatch between your Radius server and Service Shared Secret.

NOTE: You have to change shared secret on three locations.

1) Radcheck database table in Radius Server
2) /etc/raddb/clients.conf (In case of CentOS)
3) /etc/openvpn/radiusplugin.cnf

This will solve your issue. For more understanding you can see Defining Shared Secret on official documentation of Radius Server. link