FB detect an insecure connection from SLogin???

Hello. This is a Facebook requirement, all sites that want to use Facebook authorization must work using the HTTPS protocol.

Facebook requires https protocol on the site. You cannot request authorization if your site does not use Https.

In addition to the changes on the site, you need to reconfigure facebook applications.
Change authorization paths to https and add your site with https protocol to trusted url.
Remember that Http and HTTPS are not just different letters, they are also different domains and, as a result, websites.