I have encounter this problem once again, I have reported it to nextcloud community (https://github.com/nextcloud/server/issues/6657)
so in version 1.4 everything was fine. I now have version 188.8.131.52-ose. I use DAViCal with a debian.
My old account’s still work(sync), but when I add a new one it fails recognizing the calendars.
Thunderbird Calendar-Plugin still works and is able to subscribe calendars from DAViCal (old and new)
Ahh and Apache2 listens on 80, 8080, and 443
Thanks for your time
403 Forbidden looks like a server problem …