First, take the domain, which is simply the fully qualified host/domain of the server, for example "yourserver.domain.com". Then go to System->Service Parameters. Select the server, and then select Cisco XCP Web Connection Manager (Active). Most likely, the setting will be "/httpbinding". Then concatenate the two along with the port 7335 for the BOSH URL, as in "http://yourserver.domain.com:7335/httpbinding" or "https://yourserver.domain.com:7335/httpbinding" if you're using a secure connection.
Now try going directly to the BOSH URL. For example, go to https://somedomain.com:7335/httpbinding in your web browser (assuming you're using https).
If you're using https, and you see any sort of certificate warning, then that's a problem. In Firefox, you can create a permanent exception. If you're using Chrome and you see "Your connection is not private", you can click on Advanced and allow the exception. But you'll have this problem every time you restart Chrome because, while it's possible, Chrome doesn't make it easy to create a permanent exception.