Connect IOS to shared calendar

I’m having some difficulty getting an iphone to connect to a users additional calendar.

In settings calendar
I add CalDAV Account:
server : http://nexcloud.myserver.bla/remote.php/dev/principals/user/username/myadditionalcalendar/

then throws error and cannot connect

If i repeat process, without the “/myadditionalcalendar/” at the end it connects fine…

I understand the problem probably lies somewhere between the keyboard and chair, if someone could help me out please…

can someone tell me if this is even possible?

I got a Thunderbird under Windows client to connect to multiple calendars without issue, so suspect this may be a client side issue, but some help would be really great.

Should I direct my question elsewhere? sorry I am either an Idiot, or being ignored…