On top of what @baris said, if you are using a reverse-proxy like nginx, you can add that location to redirect to the same place.
URL Blocked: This redirect failed because the redirect URI is not whitelisted in the app’s Client OAuth Settings.
I have been trying this for a while
my config.json has the same url as the facebook dev page,
I have both client auth and web auth on, and have tried numerous attempts at different variations of everything else. and still says url blocked,
I have added a website with the URL, I have also added it to the App Domains. I don't know what else i can do.
managed to fix it by putting the ip address in the facebook url.. not the same one that is in config.json