Open the macOS Calendar app.
On the left side, find the calendar you want to access in Clockk. If you don’t see a list of calendars, click the “Calendars” button in the top left-hand corner.
Click on the wifi-on-its-side icon. You'll see a panel appear with sharing options.
Click the checkbox next to “Public Calendar”. Thanks to a bug in macOS Calendar at the time of this writing, nothing will change. Click “Done”, and then click the wifi-on-its-side icon again.
Now the share URL will appear. Triple-click the
webcal:// URL, and then choose Edit > Copy.
webcal:// URL into the “ICS URL” field in Clockk.
Name your calendar after the email address associated with this calendar.