Trouble registering WNS via partner portal

The WNS/MPNS page in Partner Center shows "visit the App Registration portal" but clicking that link returns an error page. I can navigate to certificate and secrets and create the client secret successfully.

However my Package SID doesn't appear to be registered with WNS — login.live.com/accesstoken.srf returns "Invalid client id". I need the app registration linked to my Store app so I can obtain WNS credentials.