The readme indicates muc_domain is depreciated, however I believe it is still required for private servers. Without it, as ours is not conf.hipchat.com, I receive a 400 during connection. When I set it in config, however, I do not receive a 400:
<error code='400' type='modify'><bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/></error>
I'm still working on getting this up and running, but wanted to document this for anyone else running into the same issue.