Hi Andrew Boon
I created an account in OneSignal.
I selected Webpush-Typical site setup.
I uploaded some files to the root and added code in Designer-Injections-HEAD
I also added OneSignal App ID and REST API Key in Studio-Settings-System-Push notifications.
The Notifications app already had it installed.

By entering https://tnoa.com.ar now if the notification appears. Is this one-time or are there other events that will make a notification appear?

Thanks.