Error codes of 5xx indicate server error, take a look at this list of HTTP status codes.

Now more to the point about the failure to establish an SSL connect. Since you're issuing a GET, you can easily check this url in your browser. If it works in your browser, then it might be your client.

Each browser has at least 1 good REST client dashboard, I'd use the one for your browser of choice. IMO, it's enhances the script writing experience by giving you a little more control to tinker.