I installed an instance of Ubuntu Amazon EC2 and followed this official guide for setting up the desktop and remote access from Windows:
https://aws.amazon.com/premiumsupport/knowledge-center/connect-to-linux-desktop-from-windows/
I successfully completed all the steps and installed ubuntu-desktop and xrdp as indicated in the manual.
However, I am stuck with the last step # 16, where it tells me to “insert the fully qualified name of your Amazon EC2 instance for the computer” in the Remote Desktop Connection client.
I'm not sure my "full name of your Amazon EC2 instance for the computer." I tried various combinations of my public DNS server, public IP address, private DNS and private IP address, as well as instance ID without any successful actions.
Can someone please help me figure out what I am missing here?
Edit:
This is the error I get when entering my public DNS as the full name: 
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