DNS_PROBE_FINISHED_NXDOMAIN when running a Flask app from the codespaces

[rhythmd18]

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I created a Flask application on the GitHub Codespaces. I am not able to access the webpage by running the app as the webpage does not show up and instead it throws an error: "DNS_PROBE_FINISHED_NXDOMAIN".
What's the actual issue here, and how do I possibly fix this?

[jge162]

Check the firewall settings: Make sure that the firewall is not blocking the connection to the web server.

Try to flush your DNS cache by running the command ipconfig /flushdns on Windows