I’ve been checking your website previously and about the Facebook login issue, they keep saying invalid OAuth Redirect URIs (https://www.dropbox.com/s/f9bl2dqhbbdt22h/Screenshot%202018-04-06%2010.46.10.png?dl=0).
Then i try to use my own API key and secret. It just works fine in there and you can check this video result https://youtu.be/E9odJPQhh3g.
Regarding this thing, please try to enable Client OAuth Login and Web OAuth Login option. Also, may I know what API Version that you use?