It looks like the
Nginx server is not configured on your ROSbot.
Check contents of
sudo nano /etc/nginx/sites-enabled/default
When following the tutorial, it should have had edited line:
If you have it already edited, there is nothing to change.
To exit text editor press: “Ctrl + x”, “y”, “Enter”
sudo systemctl restart nginx
Nginx was not running, it will be started with this command.
Now you should be able to view the interface.