I added Facebook as an IDP to my Okta app and vice versa.
I followed the instructions here - Create the Authorization URL | Okta Developer
My URL successfully takes me to a facebook login, where I log in and all that works. When I get redirected back to my site however, it does not seem like I was authenticated.
In the URL though, I do see a #id_token=(giant long string) and not really sure what that does.
I currently also have a standard Okta custom login from this guide that works perfectly at the moment.