I'm just starting to experiment with the API as well. But I'm not getting that specific error on that url, so perhaps it's that there's something wonky with your API key activation.
Having said that, that specific query returns no results, even though it's in the docs as working.
Since the query below, with full name and case sensitivity, works, I have to assume something's changed on the server side and the docs are a bit behind.
fwiw, it seems that some on the filter parameteres on other endpoints fail to return results even when full text is provided, so I think some things are awry at the moment.