Google Calender setup not working

I would like to buy the pro version of emclient, but I can’t seem to be able to set up google calender (just the calender, no gmail). What does it mean, I have to connect through the web interface first - when I connect to Google through the browser I still can’t connect with eM Client.
Thanks for any hint.

Hi, if you’ve not checked your calendar yet on the google interface, please login to your calendar at http://calendar.google.com and login using your credentials, this is a needed step for activating your calendar.

If the issue persists, please make a screenshot of the error you’re seeing and submit it here on the forum.

Thank you,
Paul