Why do you think that "processing" is a failure? Processing means that it's in progress, and you need to poll the order until it becomes "valid" or "invalid". Look at the flowcharts in RFC 8555 section 7.1.6.
The order moves to the "processing" state after the client submits a request to the order's "finalize" URL and the CA begins the issuance process for the certificate. Once the certificate is issued, the order enters the "valid" state. If an error occurs at any of these stages, the order moves to the "invalid" state.
You may want to look at this announcement. They don't have asynchronous finalization in prod, but they may still have it on in staging: