as a user, when I unsubscribe to a notification setting outside of the app, I see a web page indicating if it worked.

most of the unsubscribes will likely happen from within the application, however, a user should be able to unsubscribe to a notif from an email notification. When they do, they should see a page that indicates if the unsub worked or not (like standard unsubscribes from marketo based emails, screenshot attached).