To sync your Flow calendar with your favourite calendar app, click "Calendar" above the calendar view, and select "Sync to Calendar."
This will take you to a new pane where you can copy your secure calendar URL for the next steps.
Sync with Google Calendar
Open your Google calendar. Once open, click the drop down arrow beside "Other Calendars", click "Add by URL", and paste the URL you just copied from Flow.
Click "Add Calendar" to save your changes.
You can edit the name or other details of your calendar at any time in Google’s calendar settings.
You’ll now be able to see your tasks with due dates in Google calendar and any changes you make to your tasks in Flow will be reflected on the calendar. Don’t forget that editing in Google calendar will not change your tasks in Flow.
Sync with Apple Calendar (iCal)
Once you’ve copied the URL, open iCal, and in the menubar, click "File > New Calendar Subscription".
Paste the URL you copied into the empty field and click "Subscribe".
Now, you’ll see your Flow tasks with due dates in iCal.
To make sure iCal refreshes often to reflect changes, select "Calendar > Preferences > Accounts" from the menubar and set how often you want it to update.
Note that any changes you make in Flow will be reflected in iCal, but tasks edited in iCal will not change in Flow.