The issue isn't with JomSocial v4 at all. As noted, JFBConnect has been tested extensively with that release and we have many, many users successfully using that combination.
Can you please do the following:
* Go to the System Information -> PHP Information area in Joomla and take a screenshot of your curl configuration section. It should look like below:
Specifically, I'll be looking at the SSL support option and the SSL version, but there's other details that will help as well.
* Next, please let me know the *exact* error message you are receiving. That will help us look up details of what that message means.
Thanks,
Alex