It’s likely you received the 404 not found html page.
When using the API please always use .json for any api requests because while most endpoints will return json by default some will return html. Looks like this route doesn’t have a default though, so when it didn’t get passed .json the route couldn’t be found.
You really should be specifying .json so you don’t get this error page, but I wonder if we do detect an API call if we should return an actual 404 http response instead of 200 with an unreadable html body 
?