Laravel5.8 Pusher Event 500 İnternal Server Error - laravel

Question

I tring add a chat extension to my web site , watched very much video lesson, Laravel and Pusher using user. Normally website is working
broadcasting(new MyEvent('my-event'));
but if I add line -before return line- , giving 500 Internal Server Error.
sended message is saving to DB but not return value...
Please help me
My ChatEvent.php
use App\Chat;
use Illuminate\Contracts\Broadcasting\ShouldBroadcast;
use Illuminate\Broadcasting\PresenceChannel;
....
class ChatEvent implements ShouldBroadcast
{
use Dispatchable, InteractsWithSockets, SerializesModels;
public $chat;
/**
* Create a new event instance.
*
* #return void
*/
public function __construct(Chat $chat)
{
$this->chat = $chat;
}
/**
* Get the channels the event should broadcast on.
*
* #return \Illuminate\Broadcasting\Channel|array
*/
public function broadcastOn()
{
return new PresenceChannel('chat');
}
}
My ChatController.php
use Illuminate\Http\Request;
use App\Chat;
use App\Events\ChatEvent;
class ChatController extends Controller
{
public function __construct(){
$this->middleware('auth');
}
public function index(){
return view('chat.chat');
}
public function fetchAllMessages(){
return Chat::with('user')->get();
}
public function sendMessage(Request $request){
$chat = auth()->user()->messages()->create([
'message' => $request->message
]);
broadcast(new ChatEvent($chat->load('user')))->toOthers();
return ['status' => 'success'];
}
}
VueJs Post And Get codes
<script>
export default {
methods: {
fetchMessages(){
axios.get('messages').then(response =>{
this.messages = response.data;
})
},
sendMessage(){
this.messages.push({
user: this.user,
message: this.newMessage
});
axios.post('messages',{message: this.newMessage});
this.newMessage='';
},
}
}
</script>
Routes and Channels
Route::get('/chats','ChatController#index');
Route::get('/messages','ChatController#fetchAllMessages');
Route::post('/messages','ChatController#sendMessage');
Broadcast::channel('chat', function ($user) {
return $user;
});
Pusher's AppKey,Secret,ID and Cluster OK,
Broadcaster-Driver: pusher Everywhere