Unable to create event grid event subscription to an EventGridTrigger using WebHook on a function app secured by EntraId (Isolated-Worker, .NET8, C#)

Question

I am to create event grid event subscription to an EventGridTrigger using WebHook on a function app secured by EntraId

I have tried following the instructions provided here: https://learn.microsoft.com/en-us/azure/event-grid/secure-webhook-delivery

• Trigger: EventGridTrigger
• Authentication: Microsoft (EntraID)
• Subscription Type: Webhook
• Schema Type: Event Grid Event
• Identity: Yes
• App Registration role for Event Grid: Created
• App Registration role assignments: Created
• Not sure if following details matter, but including just in case:
  • Function App Version: V4
  • Function App Environment: .NET8
  • Process Model: Isolated-Worker
  • Package Versions:
    • Microsoft.Azure.Functions.Worker: 1.22.0
    • Microsoft.Azure.Functions.Worker.Sdk: 1.17.2
    • Microsoft.Azure.Functions.Worker.Extensions.EventGrid: 3.4.1

And i received the following error (Note function URL masked):

Webhook validation handshake failed for https://****************************.azurewebsites.net/runtime/webhooks/EventGrid. Http POST request failed with response code Unknown. For troubleshooting, visit https://aka.ms/esvalidation. Activity id:2e1a9e4f-b335-4e34-82d4-1b3fe0e728ea, timestamp: 6/4/2024 3:47:54 AM (UTC).