App does not work properly. What to do
99% All issues is from the wrong settings.
1. Check where you have instaled SSL. It is important if you have SSL installed on domain somedomain.tld or www.somedomain.tld. If you have SSL on WWW version check that all URLs are with https:// and with WWW
2. Check if your server have PHP version 5.3+
3. Check the APP ID and APP Secret in Install form
4. If you see error code 404 check the .htaccess file on root domain if is not some restriction inside.
5. Check if is Sandbox mode in Facebook developers disabled.