The Google Calendar integration function is currently unavailable because Google is checking this app.
If you want to sync with Google Calendar, please use the following method instead.
1. Show Google Calendar events in iPhone Calendar
Please refer to this page.
https://support.google.com/calendar/answer/99358?en=us&co=GENIE.Platform%3DiOS&hl=en
2. Select Google Calendar as sync destination with this app's iOS calendar sync function.
The calendars in the Google account added in step 1 are also displayed in the list, so select the calendar you want to synchronize.