// config/app.php
'providers' => [
    ...
    NotificationChannels\OneSignal\OneSignalServiceProvider::class,
],

// config/services.php
...
'onesignal' => [
    'app_id' => env('ONESIGNAL_APP_ID'),
    'rest_api_key' => env('ONESIGNAL_REST_API_KEY')
],
...

use NotificationChannels\OneSignal\OneSignalChannel;
use NotificationChannels\OneSignal\OneSignalMessage;
use NotificationChannels\OneSignal\OneSignalWebButton;
use Illuminate\Notifications\Notification;

class AccountApproved extends Notification
{
    public function via($notifiable)
    {
        return [OneSignalChannel::class];
    }

    public function toOneSignal($notifiable)
    {
        return OneSignalMessage::create()
            ->subject("Your {$notifiable->service} account was approved!")
            ->body("Click here to see details.")
            ->url('http://onesignal.com')
            ->webButton(
                OneSignalWebButton::create('link-1')
                    ->text('Click here')
                    ->icon('https://upload.wikimedia.org/wikipedia/commons/4/4f/Laravel_logo.png')
                    ->url('http://laravel.com')
            );
    }
}

public function routeNotificationForOneSignal()
{
    return 'ONE_SIGNAL_PLAYER_ID';
}

OneSignalMessage::create()
    ->button(
        OneSignalButton::create('id')
            ->text('button text')
            ->icon('button icon')
    );

OneSignalMessage::create()
    ->webButton(
        OneSignalWebButton::create('id')
            ->text('button text')
            ->icon('button icon')
            ->url('button url')
    );