Handle device offline status

At present I am working on multiplayer game using Photon Unity Network plugin. I don't have any problem in working of this game. But I want to detect device offline status and want to display appropriate message to the player.

For this I have implemented following methods and it gets called by the server.

     void OnFailedToConnectToPhoton()
     {
         Debug.Log("OnFailedToConnectToPhoton");
     }
 
     void OnConnectionFail()
     {
         Debug.Log("OnConnectionFail");
     }

But I got following error in console that represented in following image.

How to handle condition when device not connected to internet and give appropriate message to player?