Windows client installation servername does not work

I have installed nextcloud 14.0 on webspace.
I can access files via the browser (firefox), sync contacts + calendars. Everything OK.
Access is via

Now I have Windows Client installed on laptop.
File used: Nextcloud-
If the query in the connection wizard for the server comes I enter: - then comes an error message.

The website under
may be temporarily unavailable or permanently moved to a new web address.

Also at - comes error message.
What did I overlook?

The SSL certificate is wrong