Subscription validation request failed. The notification endpoint must respond with a 200 OK to the validation request

Question

I am trying to create an Event Grid subscription to receive user notifications using the Microsoft Graph library. However, while creating the subscription, I encountered the following error: "Subscription validation request failed. The notification endpoint must respond with a 200 OK to the validation request." After researching this issue in the community, I discovered that the host header is missing in the validation request , which causes my API endpoint to be hit & server return Bad Request (400). This happens because the server blocks the request before it reaches my application. How can I successfully validate the request without the host header?