Issues with NextCloudPi setup on Debian stretch

Well, this seems to be the place for NextCloudPi issues, even though I am not using a Docker version of it. I used the debian setup script

The first time the script complained about missing php modules (saying I should ask the administrator to install them) - this is one of the jobs that I expected the script to do for me?!

however, a second try ends up with

Site nextcloud disabled.
To activate the new configuration, you need to run:
systemctl reload apache2
Site ncp-activation already enabled
useradd: Benutzer »ncp« existiert bereits

trying the mentionend command i get

Failed to reload apache2.service: The name org.freedesktop.PolicyKit1 was not provided by any .service files
See system logs and ‘systemctl status apache2.service’ for details.

If I open the website I get passwords for NextCloudPi and NextCloud (“NextCloudPi Activation”) however clicking “Activate” causes “NextCloudPi not yet initialized, trying again in a few seconds …” and some time later reports a failure.

a netstat shows, that the port 4443 is not open on the NextCloudPi system and port 443 redirects to the activation page again…

Which model RPI are you using?