Basic API issue

As I understand the API, this URL should return something:
http://my-domain/edd-api/products/?key=my-actual-key&token=my-actual-token

However this gives me a 404, both locally and on a live site. Am I missing some setting?

http://wordpress.org/extend/plugins/easy-digital-downloads/