You're missing the question mark before the query string
arguments. It should be:
.../url/short/?url=...&appkey=...
Yes, sorry, I got it wrong in my reply.
That endpoint doesn't take a "url" argument. Rather, the path part
of the Digg short URL is the last term in the endpoint path. So the
correct request is:
http://services.digg.com/url/short/d12BRu?appkey=http%3A%2F%2Fwww.smnlikdat.org
That is, the endpoint is:
/url/short/d12BRu
Yeah, and an example wouldn't hurt. Sorry for the confusion.