Currently there seems to be no proper way to return a non-200 response on a webhook endpoint.
Ideally you could return a body with a specific http status code, something along the lines of the Response.json() function for remix.

An alternative approach that I think would also be enough and quicker to implement would be to catch all errors being thrown in a webhook handler and just return a 500 back. Lacks the option to explicitly specify the http code, but it allows to at least differentiate between success and error cases for the response