The error message actually says very precisely what the problem is, namely that there is no public IP address available for your Anschluss.
Technically the problem is that Swisscom has activated CGNAT on your Anschluss and you now have to get support to turn this off again on your contract.
Only the hotline or myService can do this (usually without charge).
As soon as CGNAT has been deactivated, you will also be able to set up the DynDNS and the VPN connection.
Hobby-Nerd ohne wirtschaftliche Abhängigkeiten zur Swisscom