SDX pro is not authenticate using VRRP IP to Windows Radius server

My client has SDX PRO setup in high availability mode and they want to authenticate some user to access using windows Radius server.
I configured Windows Radius server and do the setting in the SDX pro also but problem peplink cannot when i using vrrp IP in the radius server user cannot be able to login but when i changed the IP to the master device user immediately login.

can someone to explain why peplink not authenticate with VRRP IP to radius.