Hello,
There isn't a chat plugin section anymore because Facebook discontinued their support of the plugin that they had previously. None of the steps that you did previously would apply anymore, and there isn't a button action to have chat on the same page anymore. There is a Messenger Widget action still:
This will display an initial greeting message, but it will then redirect to Facebook to have the chat session since they no longer support a plugin that can be used to chat on your site without redirecting. None of the previous whitelisting etc is needed though, since that was related to the plugin that they no longer provide.
Hope that helps!
