handshake validation issue while creating event subscription in Azure communication service

Question

Deployment has failed with the following error: {"code":"URL validation","message":"Webhook validation handshake failed for https://webhookappfunction.azurewebsites.net/api/WebhookFunction. Http POST request failed with response code Unknown. For troubleshooting, visit https://aka.ms/esvalidation. Activity id:f9db901a-d685-4034-9155-aa0a13d2a335, timestamp: 3/7/2025 1:50:30 AM (UTC)."}

Answer 1

Hi Megalai Sathanathan,
Thanks for the question and using MS Q&A platform.
The handshake validation issue in Azure Communication Services when setting up an event subscription usually happens because the webhook endpoint isn't handling Event Grid’s validation request properly. When registering a webhook, Azure Event Grid sends a SubscriptionValidationEvent and expects a response that includes the validationCode. If this fails, the event subscription won't be created. To fix this, make sure your webhook function processes the validation request and returns the necessary response. For Azure Functions, check for an event type of "Microsoft.EventGrid.SubscriptionValidationEvent" and return {"validationResponse": validationCode} within 10 seconds. Also, make sure your webhook URL is publicly accessible; if it's behind a VNet, private endpoint, or needs authentication, adjust network settings or use Managed Identity authentication. Ensure CORS settings allow requests from Event Grid and that the function accepts POST requests. If the issue persists, check Function App logs in Application Insights for errors. For more troubleshooting tips, see Microsoft's official documentation on Event Grid subscription validation and troubleshooting validation issues.
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