matrix-spec-proposals/event-schemas/examples/m.room.member#invite_room_state

{
  "$ref": "m.room.member",
  "content": {
    "membership": "invite",
    "avatar_url": "mxc://example.org/SEsfnsuifSDFSSEF#auto",
    "displayname": "Alice Margatroid"
  },
  "unsigned": {
    "age": 1234,
    "invite_room_state": [
      {
        "type": "m.room.name",
        "state_key": "",
        "content": {
          "name": "Forest of Magic"
        }
      },
      {
        "type": "m.room.join_rules",
        "state_key": "",
        "content": {
          "join_rule": "invite"
        }
      }
    ]
  }
}