Illuminate \ Broadcasting \ BroadcastException 404 NOT FOUND - laravel

Question

I'am using Laravel 5.8 with pusher to make an broadcast , after i submit the form im getting this 404 not found i have been searching the google for the answer but no luck.
PostPublished.php
<?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 PostPublished implements ShouldBroadcast {
use Dispatchable, InteractsWithSockets, SerializesModels;
public $data;
public function __construct($data) {
$this->data = $data;
}
/**
* Get the channels the event should broadcast on.
*
* #return Channel|array
*/
public function broadcastOn() {
return new Channel('my-channel');
}
public function broadcastAs()
{
return 'Post-Published';
}
}
AdminAnnounceController
public function store(Request $request)
{
$data = request()->validate([
'department' => ['required', 'string', 'max:255'],
'title' => ['required', 'string', 'max:255'],
'content' => ['required', 'string', 'max:255'],
'status' => ['required'],
]);
$data = Announcement::create([
'department' => $data['department'],
'title' => $data['title'],
'content' => $data['content'],
'status' => $data['status'],
]);
event(new PostPublished($data));
return redirect('admin_announce')->with('success', 'the Annonucement has been send');
}