So I made this FB app with iframed website with the help of Woobox. As it turned out, I needed SSL domain in order for iframed site to display for everyone, even those with secure browsing enabled. So I went ahead and got Hostgator Business account that comes with free RapidSSL for one domain. As I understand, everything is set up, SSL online checks verify my domain, browser & facebook still sees it as untrusted. I flushed my DNS. I'd be very thankful if anyone who've ever done this would contact me and help out a bit! Nevermind! After 24hours everything magically started to work!