Set up like so: https://support.zendesk.com/entries/382630-hipchat-integration
Add the target here: http://support.YOURDOMAIN.com/settings/extensions#targets
Set up the trigger here: http://support.YOURDOMAIN.com/rules?filter=triggers
Possibly we had to put something ("x") in the trigger action message, even though the instructions above gave the impression you could leave them blank.
We used this for the request URL: