How to Make Webhook Processing Idempotent in .NET

Introduction Webhook endpoints are not guaranteed to be called only once. In fact, most payment providers and third-party services automatically retry webhook events if: Your API times out Your server returns a non-2xx response Network issues occur If your .NET application is not idempotent, duplicate webhook calls can cause: Duplicate orders Multiple status updates Data corruption Inconsistent business logic In production systems, idempotency is not optional — it is essential. In this guide, we’ll walk through how to implement idempotent webhook processing in .NET (ASP.NET Core). What Does Idempotent Mean? An operation is idempotent if executing it multiple times produces the same result as executing it once. For webhooks, this means: If the same event is delivered twice Your system processes it only once The Core Problem Most webhook payloads include a unique event identifier, such as: event_id transaction_id payment_reference If you ignore this identifier and simply process the requ