User Sync is not syncing users

I am getting this error message on my sub site when trying to use the User Sync plugin, it works fine on the master site.
There was a connection problem. Please check the URL and Key of the Master site.

Master: http://ehotelierhub.wpengine.com/
Sub: http://ehnews.wpengine.com/

I have tried copying the URL and Key, but it still fails. My sites are hosted on WPEngine.

Support access is enabled, suggestions?