That error message means that your web server’s IP address has been blacklisted by Facebook, most likely because someone else using the same IP address has violated the Facebook Terms of Service. If you’re on a budget web hosting plan then you most likely share your web server with hundreds, if not thousands, of other websites. As you all share the same IP address then if one of those website’s has the IP address blacklisted/blocked by Facebook then all of the websites on the server are also blocked. The only way around this is to contact your web hosting company and ask them to either change your IP address or move you to a different web server. If your IP address is blocked by Facebook then there’s nothing we can do on our end unfortunately as the plugin isn’t able to connect to Facebook to retrieve your posts.