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 > Other Calendars > Add by URL > paste iStudiez Pro Calendar URL
Google Calendar refreshes data within 24-48 hours, thus, it may take a time to show iStudiez Pro events you have recently added in Google Calendar.
There is a possible solution.
Please read more here.