Hi Nikola I had exactly the same problem than here https://easy-appointments.net/support/error-message-when-trying-to-add-more-than-one-calendar-within-google-calendar-add-on/ and I tried everything you adviced... Last week, everything worked rather well on my website for testing: Google back sync 2 ways was ok, I just had problem with cancelled appointments due to #linkcancel# and attached ICS. Because of that, I had 3000 appointments, and I decided to uninstall the plugins to start from scratch and to have a cleaned installation... I had to authorize at least 4-5 times and finally, it was ok but other issues began : cron failed once under two, overlapping time from Google calendar ... I uninstall, re-install plugin EA and EA connect, cleaned database, I removed connection to app, changed Client secret, created 3 new projets in Console Developers to start from scratch, changed my Browser, flushed cache navigator, cache server... At least 10 hours to find a solution and I lost hope... :-( Please what can I do now ?