sql server: configure SSRS remotely: a connection to the computer can not be established

I just installed the new SQL Server Reporting Services 2017 following these instructions:
https://docs.microsoft.com/en-us/sql/reporting-services/install-windows/install-reporting-services?view=sql-server-2017

I have a Windows server with SQL Server Express 2017.

I need to set up the report server remotely, but when I try to find the server from the Report Server Configuration Manager, it simply says that I can not establish a connection to the computer & # 39; (view image).

Report Server Configuration Manager

I tested this configuration on two separate computers outside the domain (to configure remotely), and it worked fine, but it does not work on the server that is inside the domain.

I added my user for permissions with these steps here:
https://docs.microsoft.com/en-us/sql/reporting-services/report-server/configure-a-report-server-for-remote-administration?view=sql-server-2017

But it still does not connect, any idea of ​​what's missing?

I also looked at this question, but I could not find much help:

Unable to sign in to Reporting Services through SSMS and the Reporting Services configuration administrator