If you use virtualmin, then you have to change the Scylla port from 10000 to 10001, because virtualmin uses that port for the panel.
Also, check that that port is open and that the firewall is not blocking that port.
Go step by step through the documentation and everything will work for you.
Also in scylla config you have to add this:
nano /etc/scylla/scylla.yaml
Locate the authenticator: line, uncomment it, and change it to:
authenticator: PasswordAuthenticator
api_port:10001 (or another free port that is not occupied)
Here you have everything in more detail:
https://support.mash3div.com/hc/articles/17/21/96/installation
Good luck!