Currently, the only errors that users get when something is wrong, is when they try to request a url and get back "Sorry, we were unable to retrieve a call url." We need to do a couple of things: 1) Try and explain why 2) If registration has failed when the user starts up, (i.e. they have outstanding call urls that could be activated), then we need some way of informing them that they aren't going to be receiving calls.

Is this a duplicate of https://bugzilla.mozilla.org/show_bug.cgi?id=1002416?

Yeah, most likely, if not we can always re-raise it.