Broadcast Exception with laravel pusher -

i'm using pusher laravel 5.4 . installed pusher using : composer require pusher/pusher-php-server "~2.6" after make necessary changes in .env , config/app.php , config/broadcasting.php . create taskevent :

<?php namespace app\events;  use illuminate\broadcasting\channel;  use illuminate\queue\serializesmodels;  use illuminate\broadcasting\privatechannel;  use illuminate\broadcasting\presencechannel;  use illuminate\foundation\events\dispatchable;  use illuminate\broadcasting\interactswithsockets;  use illuminate\contracts\broadcasting\shouldbroadcast;   class taskevent implements shouldbroadcast  {    use dispatchable, interactswithsockets, serializesmodels;      /**      * create new event instance.      *      * @return void      */      public $message;     public function __construct($message)     {         $this->message=$message;     }      /**      * channels event should broadcast on.      *      * @return channel|array      */     public function broadcaston()     {         return new privatechannel('testchannel');     } } 

then , in routes/web.php :

use app\events\taskevent;  route::get('event',function(){     event(new taskevent('hello world')); }); 

but i'm getting error :

(1/1) broadcastexception  in pusherbroadcaster.php (line 106) 

please me !!!