This calendar https://accueil.iut-info.univ-lille.fr/calendrier/iutinfo.ics return the error “Couldn’t parse iCalendar”.
I’ve tried to validate it with https://icalendar.org/validator.html and i get no errors. And I can open the file directly with the calendar of my Samsung phone.
I don’t know how much can I try to debug. Can you help me with that ?