Hi
Here's another reason to migrate to HTTPS if you haven't done so. Or double check your certificate settings.
A new “Enforce HTTPS†setting for Facebook Login is now available.
All new apps created since March 2018 have already been required to use this setting, and existing apps and websites using Facebook Login have until October 6, 2018 to opt in before it will automatically be enabled. Any insecure redirect URIs or pages making Login or API calls with the JavaScript SDK from HTTP pages will stop working after that date.