Holy moly. They changed the interface slightly back in July, and we knew we needed to update the guide. However, I just looked again, and yes, it's completely different.
It looks like the main settings you'd need to ensure are correct are in the "Web Site" tab. Make sure website url and possibly base domain are set. If your site is located at
www.example.com, you'd want:
URL:
www.example.com
Base Domain: example.com
The reason the 'next' error is appearing above is generally when you redirect someone to Facebook to log in, Facebook requires that they be redirected back the application's website. We take care of telling Facebook where to redirect them back to, but if the URL or base domain doesn't match, you'll get that error.
Hope this helps, and we'll get on updating that guide! Thanks for pointing it out.