I'm the person from that link, and in my case, I hadn't noticed the parameter exlimit, which was the real problem. If exlimit is set, but exintro is not, at least you get a helpful warning; if exlimit isn't set, then it just fails without warning (this is what happened to me). A sufficient fix might be to either draw more attention to the exlimit param in the documentation, and/or give a warning in the returned data if multiple titles were specified but exlimit was not set.

The registration page looks great, but is the accommodation cost (e.g. 240 Euros for a single room) nightly or total? If it's total, what date range does it cover, and does it include the registration fee?