Wpf Permissions for Push Notification Sample

I am trying to make Push Notification work in WPF. I am using https://webpushdemo.azurewebsites.net/ to test the notification but it is throwing "Uncaught (in promise) DOMException: Registration failed - permission denied" error.

I have tried to hook the PermissionRequested event but it is not triggered.

Maybe an example on how to do it should be added to the sample project. 