hi Bill,
How can I check that the hub shares my app's view of the subscription status (that I am subscribed to the feed)?
this depends on the hub that you are using. If you use the google reference hub "http://pubsubhubbub.appspot.com"; you can check at "https://pubsubhubbub.appspot.com/subscribe"; whether you are subscribed to a specific topic. Other hubs have probably not such an option.
What else can I do to find out what the problem is?
If you are unsure whether you are subscribe to a topic simply send an subscription request to the hub and look at the http response code ... HTTP 204 means that your subscription is active HTTP 400 or 500 if there is an error with your subscription.
best regards Christoph
