Webhook returns 204 even when a parsing error occurs

[kumada626]

What happened: When a parsing error occurs during the webhook parsing process, the response still returns a 204 status, making it difficult to notice that an error has occurred.

What you expected to happen: The system should correctly return a 500 or 400-series error, making it easier to notice when an error occurs.

How to reproduce it:

1. Send a webhook that will cause a parsing error.
2. Observe that the response returns a 204 status instead of an error status.