Please, see the nsdc machine journal. Perhaps you'll find more about the provisioning error...
journalctl -M nsdc
The -M flag should work also with systemctl:
systemctl -M nsdc status samba-provision.service
There are no credentials for it. Even if you get a shell with the following command, you'll get a minimal system because the chroot is only samba+its dependencies:
systemd-run -M nsdc -t /bin/bash