Problem adding public iCal calendars' URLs to eM Client

How to add public ical calendars with holidays? I have tried to add calendars form a couple of pulicly available sources to eM Client. However, I always get the message “please enter a valid caldav url”. Here are a few example of URL that don’t work with eM Client but work perfectly on Apple devices:



we can import this one-time, but we can’t update it continuously.