When you first visit this page, you will be prompted to allow or block notifications. If you allow, you will be added to the notification list and will receive a welcome notification.
After you allow notifications, you can send a notification from eg Appmixer flow or directly from the OneSignal dashboard.
Important: keep only one tab with this website open, close developer tools or bypass network
Based on: https://github.com/OneSignalDevelopers/OneSignal-PushNotification-JavaScript-Sample