Configuring the Google Contact/Calendar Add-in for different users

Configuring the Google Contact/Calendar Add-in for different users

We have a number of users in our Zoho CRM, each with their own Google Calendar, which we need to sync with their user. When I log in as each user, and try to configure the app ( I have the Google Account authentication credentials for each user), then when I try to select a calendar for syncing, it only shows me my own calendars  (I'm the Super Administrator and I performed a calendar sync to start things off). Why is this happening, and how can I resolve it?  I've got to get this working by Tuesday!!

Thanks in advance for your help.

Best,

Yehoshua Kahan.