Your App domain must match the domain from the Facebook Web Games Page URL, Mobile Site URL, Site URL, etc. Please check the other settings for those URLs listed to make sure there are valid URLs with matching domains as well and see if the error is resolved once you add them. Additionally, you may want to go into the JFBConnect backend and use our Autotune Configuration Tool. In the Facebook tab of Autotune, you should be able to see recommendations on what to set the settings to. Hopefully this should help you to move forward, but let us know if you continue to have trouble figuring it out.