Yesterday afternoon Facebook sent out a reminder to developers to adjust their code as part of the shift to iFrames. Rather than using GET, developers must use POST.
For PHP developers, using $_REQUEST will theoretically work as well although it’s three more letters to type. The change will take place on Saturday so you’ll need to be ready by then. In order to get set up, all you need to do is head over to your application settings and enable “POST for Canvas” within the advanced tab. While there’s a good chance you’ve already made the change, now is a good time to make the updates.
While should be nothing more than a simple find and replace, every minor change always seems to result in some sort of bug so get your testing complete sooner rather than later. For the full details check out Facebook’s latest developer post.