Yes, your understanding is correct. There is a fundamental incompatibility between Microsoft Graph API's webhook validation requirements and Prefect's webhook implementation. Here's why: 1. Microsoft Graph Requirements: - Sends a validation request to your webhook URL - Expects a 200 OK response - Requires the validationToken to be echoed back in plain text 2. Prefect Webhook Limitations: - Always returns 204 No Content (cannot return 200 OK) - Cannot dynamically respond with different content - Not designed for interactive validation handshakes This means you cannot use Prefect webhooks directly with Microsoft Graph API subscriptions. However, there are potential workarounds: 1. Use an Intermediary Service: - Set up a small web service (like Azure Functions, AWS Lambda, or a simple Flask app) - Handle the Graph API validation in this service - Have this service forward the actual notifications to your Prefect webhook 2. Alternative Integration Approaches: - Use Microsoft Graph SDK to poll for changes instead of webhooks - Use Azure Logic Apps or Power Automate to handle the webhook validation and then trigger Prefect flows The limitation is by design - Prefect webhooks are purposefully simple event receivers rather than full-featured HTTP endpoints. For scenarios requiring complex handshakes or custom responses, you'll need to implement an intermediary layer to handle those requirements before forwarding events to Prefect.