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 $details;
    protected $link; 

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

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

    public function toDatabase($notifiable)
    {
        return [
            'details' => $this->details,
            'link' => $this->link
        ];
    }

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

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