Please note that from August 1, 2018 we need to submit the facebook app for approval and we can use the facebook app, only after getting the approval. The app submission details are available in
How can I create Facebook application?
We have introduced an alternate solution and it is a paid service starts from USD 10 per year.
So there are 2 options, use the free facebook approved API or use the paid alternate solution.
If you are using the facebook approved free API, we can use it in https sites only.