Hello, Calvin
I suppose you are implementing the Dialogflow ES Web Demo by following this Quickstart guide on Interactions with an integration[0].
I understand that after you enabled the Web Demo integration, the URL provided by a dialog window to the web page where the integration is hosted, is returning a 404? Please let me know if my understanding is wrong.
So far, I have seen a number of implementations following the steps highlighted in the article[0] without getting a URL that returns 404. Can you please confirm that you had a valid Dialogflow ES agent[1] before attempting to enable the Web Demo integration?
[0]https://cloud.google.com/dialogflow/es/docs/quick/integration
[1]https://cloud.google.com/dialogflow/es/docs/quick/build-agent