Sending a notification with an observer

  private Opportunity $opportunity;

    public function __construct(Opportunity $opportunity)
    {
        //
        $this->opportunity = $opportunity;
    }

    public function via($notifiable): array
    {
        return ['broadcast', 'slack'];
    }

    public function toBroadcast($notifiable): BroadcastMessage
    {
        return new BroadcastMessage([
            'opportunity' => 'Checkout this new opportunity: '.$this->opportunity->title."\n".$this->opportunity->url,
        ]);
    }

    public function toSlack($notifiable): SlackMessage
    {
        return (new SlackMessage)
            ->content('Checkout this new opportunity: '.$this->opportunity->title."\n".$this->opportunity->url);
    }

    public function toArray($notifiable): array
    {
        return [];
    }

   public function created(Opportunity $opportunity): void
    {
        $opportunity->notify(new OpportunityNotification($opportunity));
    }