Thank you for your feedback!
Sorry for the late reply.

I’ve tested to find that sometimes it fails to connect due to cache, but it can be solved as follow:
1. Go to Settings of web version (https://i.doit.im/home/#/settings/account) and click “Unlink Google Cal”;
2. Sign out Doit.im;
3. Close the browser and open it again;
4. Sign in Doit.im again;
5. Then Link Google Cal again.

When link Google Cal, please remember to click two buttons:
1. Click “Link to Google Cal, which is used to sync tasks in Doit.im to Google Cal;
2. Click “Modify the reverse-synced calendar lists”, and choose a calendar of Google Cal, which you may use to sync tasks from Google Cal to Doit.im.

Having finished the above settings, you may see the two sides can sync each other’s tasks. If you want to see the latest data of Google Cal in Doit.im, just click “Sync GCal”. It’s because there are quotas for Google’s sync, that is, it is unable to transmit data automatically to other apps from time to time.

If any further questions, please feel free to contact us.
Nice day!