@Matthew Adams: Hmm. Your subdomain shouldn't be the issue. What error are you seeing when you click "Connect with Facebook"?
Make sure you have a Facebook Page as well as admin or manager permission on that page. Also, make sure your browsers are allowing pop-ups and 3rd-party cookies. You could have a browser extension that is messing with the authentication.
Try deleting your browser cookies, uninstalling the App and trying to install again. Let me know if that helps!