Call Event when one user calls another user so that Bot can be added to call

We have developed our Bot application and can record all media(audio, video) locally when a user directly calls the Bot User.

However, we do not get a call event when one user calls another user - so that we can add the Bot to record the call.

Both users have the global default compliance policy which allows recording.  We have provided the necessary permissions to the Bot.

What are we missing ?  

Thanks