Ok So better to continue in the forum, given that the 9002 and 9003 pages are accessible from the outside as well as I can solve the problem of the addition of the servers?

Well,

Lets start with: do you use a password less then 25 charracters? and without special chars that could be used in development?

Secondary: any customizations to IIS?

Third: did you try and run the Powershell command to install all required IIS Features from the following guide:  https://solidcp.com/kb/installation/install-solidcp-standalone-server-within-5-minutes/

Last but not least: Can you double check Windows Authentication is disabled for the SolidCP Server website? for some people i have seen it cause issues.

My password consists of 8 digits and there are no special characters, I tried to format directly on the server and to follow that guide but gives me the same error in IIS there is no customizations, I checked several times that Windows authentication is disabled in the server and enterprise server bindings must leave the ip 127.0.0.0 or change it to the external ip of the machine (as I always do)?

You can't place the pass directly in the web.config, the Web.config pass is encrypted.

Most easy way to reset password is to use the installer --> select SolidCP Server --> settings, it will ask to reset password.

ip can be 127.0.0.1 if the portal / enterprise is on the same server, external ip or any ip is also possible depending on what you need for connection.

Ok, so I was right to change the IP with the external one, now I have tried to reinstall Windows and after installing solidcp from scratch, but I still have that error, what should I do?