Issue with FB login

Hello,

I am using the plugin on a multisite installation, but activate it only on a single “subsite”. In my opinion I have created the FB App correctly and entered the requested values into the plugin settings.

When I am trying to log in via Facebook, I get this error message:
Facebook SDK returned an error: Failed to connect to graph.facebook.com port 443: No route to host

Any idea where this comes from?
Thank you

WPB