I follow the facebook connect instruction (https://help.forumotion.com/t73698-facebook-connect), step by step. and then to the last, after I click save. That message appear. I asked my friend to try on her computer too but it was the same. I want my forum can have feature of connecting with facebook, or member can register via their facebook account easily.
It couldn't be... I tried many times, read the code carefully. I even tried to create one more ap, tried different id/ different secret code, it still didn't work.
Did you take the app off of development/testing mode? If not, this is probably why it is not working, you need to make sure the app is public, or else the forum ap wont be able to connect the facebook connect feature to the app correctly.