Error Windows Live SDK applications - Generate Package SID and Client Secret for OneSignal push notifications

Question

as already reported here:

https://twitter.com/windowsdev/status/1260710111951171584
https://twitter.com/SviluppoMania/status/1332370576023953411
to WindowsDev assistance on Twitter, I have problems with the App in https://apps.dev.microsoft.com (Live services), Live Applications SDK.
As I have a UWP App present in the Windows Store: (SviluppoMania)

With this App I use the Push Notifications provided by OneSignal.

Following their guide and your guide in generating the SID Package and Client Secret of my published UWP App, going to Product Management -> WNS / MPNS -> Live Services (previously mentioned), I have an error:

The application was not found

The application no longer exists or is not associated with your account.

The problem is not OneSignal, the problem lies in the Live Services, my UWP app exists and is correctly published, but the related Live SDK Application for the Client Secret and the Package SID does not exist as per the attached photo.

I tried creating another Windows Store application and going to WNS / MPNS (Push notifications) -> Live services site -> My applications -> Live SDK applications, I tried to click on "Link to different app" but it doesn't open in any screen.

There is no App in the Applications Live SDK connected to the Windows Store App (as per attached photo, error) and nor can I connect a new App in the Applications Live SDK to the old App published in the Windows Store.

How can I solve it?

Attached images:

1. Push Notifications
   

2. Error

3. App

Can some Microsoft Windows Developer expert add a Live SDK Application and associate it with my UWP App (mentioned above)?