When you try to login via FB see the error:
URL blocked: could Not execute the redirect, because the target URI is not included in the white list in the application's "Client OAuth settings". Make sure that the login using the OAuth enabled for both the client and web forms, and add all domains of your application as a valid redirect URI for OAuth.
Version Of Bitrix - 17.5.13
App settings :prntscr.com/jaefs1prntscr.com/jaeg5g
Domain, URL-site address specified.
What else does he need ?