I think by default Webmin in debian will only allow a local https connection. you need to edit the webmin config to allow remote hosts to connect.
Log in to webmin from the local machine go to WEBMIN CONFIG -> IP ACCESS CONTROL it's probably currently set only for 127.0.0.1 add in your local subnnet or the specific IP of your workstation if it's static.. or if security isn't abig concern you can check the box that says, [ ] ALLOW FROM ALL ADDRESSES
If theres no GUI on teh webmin machine you can use teh text browser lynx to make the change
lynx
https://127.0.0.1:10000
