Further documentation as to the use of 'callee'

As per the documentation below I noticed that the object ‘callee’ can be injected into a JWT payload to bring up an additional user interface, for when a 1-1 call is established.

However once I attempt to append this token to the URL no such UI appears.
I cannot find anything obvious in the config files as to enabling this feature…

Has it been deprecated and therefore no longer a feature?
I have additionally attached a copy of my payload below… am I doing anything wrong here with regards to the ‘callee’ object?

{
  "context": {
    "user": {
      "avatar": "",
      "name": ""
    },
    "callee": {
      "avatar": "",
      "name": ""
    }
  },
  "moderator": false,
  "aud": "jitsi",
  "iss": "",              
  "sub": "",    
  "room": "*"  
}