Hi Alex,
What is the URL in the browser when you receive that error?
What callback/redirect URL for Domino did you use when registering your OAuth client on the Connections server?
My guess here is that the scheme's don't match. The Domino server with Shindig is likely generating a callback URI with https while the OAuth client was registered with http. Connections will reject the request because the request is proving a callback URI that doesn't match the one with which the OAuth client was registered. Once we confirm this is the case, I can provide more information on how to resolve this issue.
Thanks,
-Stanton