Two way sync with google calendars not working.

For my client when one of his customers creates an appointment it will block off the time frame on the plugin, and book the appointment on his google calendar like wanted. When the client books an appointment himself on his own google calendar it does not block off the time or create the appointment within the plugin. Under users I have the setting set to sync both ways but it does not appear to be doing this. Any idea on why this might be working one way but not the other with the settings as they are now?? Thank you for all your help!