Configuring CalDav/Cardav with nextcloud and EmClient

Hello everyone
I think i need some help, cause im stuck with my config again.

Im trying to get eM Client to sync calendars via CalDav/Carddav with Nextcloud
Using the following config url

With hostname being the servers local IP adress
eM Client returns an error: Synchronisation failed, subfolders not found.

Server is https
its not routed on to the internet
hosted on a raspi 3

Syncs nicely with 3 android phones for different 2 useres

I tried the same with Thunderbird and Cardbook
Not working either .
Verification failed

Using Thunderbird this works for me:

replace username & calendar with the users name, and the name of his calendar.