It looks to me like the Realm Cloud end-point address isn't actually set correctly. Could you post the code fragment you're using that you're using to open the Realm (and the values of your realm auth and sync URLs)?
Typically a Realm Cloud endpoint address would look like this:
https://myAppName.us1.clould.realm.io - Additionally, Realm Cloud connections are done over https (port 443) and not via unencrypted HTTP (port 80).
David Spector, Product Manager, Realm, Inc.
148 Townsend St, San Francisco, CA 94107
firstname.lastname@example.org 631-827-3132 http://realm.io