Lightning Ubuntu sync doesn't work

I’m using Ubuntu 18.10 and Thunderbird 60.3.0 (64-bit) with lightning plugin and Nextcloud 14.
I have setup my personal calendar with the personal caldav link (not the global caldav link)
It never opens a window for adding my username / password and int never sync my appointments.

I have also tried TBsync add on. It’s syncing my adressbook very well, but not the calendar.

How can I sync my calendar with lightning. By the way, under "Security I only find “sync-Client Linux” not more.