Ultimate Facebook - FB to site comment issue

We're having a problem integrating this plugin to display facebook posts on the sites comments.

We've followed the setup video. Created facebook app successfully, enabled extended permissions. Checked all plugin settings.

Comments on the web site display on facebook ok, but facebook comments do not display on the site. We've manually imported comments (via option in plugin settings) and allowed 24 hrs, but nothing displayed.

We've disabled all plugins and reverted to twenty fifteen theme to eliminate conflicts, but this made no difference.

WPMU support access is enabled.

Please advise/assist . Thank you.