After installing TLHJ in Google Cloud, I cannot access to the external IP

Hello everyone. I am working on a data labeling project in my organization and I need to share with my team a little Jupyter application that I have programmed. Considering we work with private data and less than 20 people will use the application, TLJH seems the ideal choice for this purpose.

I decided to install TLJH in Google Cloud, so I followed the instructions given here: Installing on Google Cloud — The Littlest JupyterHub v0.1 documentation

I created a server in Google Cloud and I have an external IP address, but I cannot access to JupyterHub simply copying the external IP to the browser, as indicated here:

And I get a ERR_CONNECTION_REFUSED all the time.

Maybe I need to do some firewall configuration, but I am not neither a DevOps, Cloud expert, etc, so I would really appreciate any help.

Thank you very much.