This is the correct configuration if nextcloud is configured without virtual host.
If nextcloud is configured with a virtualhost, make sure to add the host name as alias of the server (otherwise name resolution could not work) and add the same name to “Trusted domains” inside Cockpit Nextcloud app.
In this case, the correct configuration is (just tested):
If you are not on one of this situations, pllease help us to help you 
Share your nextcloud config and report back the webtop log and nextcloud log.