ChatController.php

// app/Http/Controllers/ChatController.php

...
  protected $client;
  protected $channel;

  public function __construct()
  {
      $this->client = new StreamClient(env("MIX_STREAM_API_KEY"), env("MIX_STREAM_API_SECRET"), null, null, 9);
      $this->channel = $this->client->Channel("messaging", "chatroom");
  }

  public function leaveChannel(Request $request)
  {
     return $this->channel->removeMembers([$request->username]);
  }
...