exchange/app/Notifications/BookingUpdated.php

<?php

namespace App\Notifications;

use Illuminate\Bus\Queueable;
use Illuminate\Notifications\Notification;
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Notifications\Messages\MailMessage;
use Illuminate\Broadcasting\PrivateChannel;
use Illuminate\Notifications\Messages\BroadcastMessage;
use App\Booking;

class BookingUpdated extends Notification
{
    use Queueable;
    protected $booking;

    /**
     * Create a new notification instance.
     *
     * @return void
     */
    public function __construct(Booking $booking)
    {
        $this->booking = $booking;
    }

    /**
     * Get the notification's delivery channels.
     *
     * @param  mixed  $notifiable
     * @return array
     */
    public function via($notifiable)
    {
        return ['database', 'broadcast'];
    }

    // /**
    //  * Get the mail representation of the notification.
    //  *
    //  * @param  mixed  $notifiable
    //  * @return \Illuminate\Notifications\Messages\MailMessage
    //  */
    // public function toMail($notifiable)
    // {
    //     return (new MailMessage)
    //                 ->line('The introduction to the notification.')
    //                 ->action('Notification Action', url('/'))
    //                 ->line('Thank you for using our application!');
    // }

    public function toDatabase($notifiable)
    {
        return [
            'booking_id' => $this->booking->id
        ];
    }

    /**
     * Get the array representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return array
     */
    public function toArray($notifiable)
    {
        return [
            'booking' => $this->booking,
        ];
    }

    public function toBroadcast($notifiable)
    {
        return new BroadcastMessage([
            'booking' => $this->booking,
        ]);
    }
}