"solved" How to secure ISPConfig3.2 panel?

Thanks to all for helping:
Had to wait for a week because I exceeded the limit for letsencrypt.
1- changed IP address to have the public on the server.
- in case somebody needs to do that: changed IP in
/etc/hosts
/etc/netplan/00-installer-config.yaml
searched and replace ip in dbispconfig
2- requested the certificate, works solid.
3- ispconfig_update.sh --force
voila !!!
all issues closed and server is perfect ;-)