LOG IN to your Caltrics account
Hover over your logged in account name and click/tap MY ACCOUNT
The calendar link, the ics file, is the first webcal URL, immediately below ‘Your calendar connection link is:’ (NOT the second one that contains your email address!).
Copy the webcal URL using ‘Copy link address‘ (if you just ‘Copy’ the URL, ensure that you copy the exact URL with no leading or trailing spaces).