Best of all to add a Calendar URL from iStudiez Pro to Google Calendar is from your PC/Mac. 

Do the following to export classes and exams from iStudiez Pro to Google Calendar:

1. Go to iStudiez Pro > Settings/Preferences > Sync > enable the option > sign in to your iStudiez Pro Cloud sync account

2. Go to iStudiez Pro > Settings/Preferences > Calendars > enable the option > Advanced > copy Calendar URL

3. Go to Google Calendar > Add Calendar > From URL > paste iStudiez Pro Calendar URL

NOTE:

It takes up to 24-48 hours for Google Calendar to refresh the Calendars. 

Thus, it may take a time to show iStudiez Pro events you have recently added in Google Calendar. 

We, iStudiez Team, are not able to affect the time required for Google to refresh the Calendars.

There is a possible solution. Please read more here.