Fix facebook app so it appears correctly on iframe tab

Hi, we have an application that works correctly outside of facebook on it's testing environment but it won't work in a facebook iframe tab it just shows up as blank page for any user that is not a tester or a developer. Also it's set to be live and not in sandbox mode. The following error appears on Chrome: Refused to display '[login to view URL]…reggs%2Findex.php&state=5bc5dd5ee0031aef9b5fab940d824442&sdk=php-sdk-3.2.3' in a frame because it set 'X-Frame-Options' to 'DENY'. However the server is setup to allow Iframe embedding.