Not an expert in Rest api, but PSO uses some internal id’s you can see in different areas. For instance on the scheduling dataset you can see the latest internal id. I think these are the same id you can see in the audits table. So I would expect that such a returned internal id can be traced in audits or failed audits.

Just to add to this, the last internal id processed is also included in the plan row in the output (input_reference_internal_id), so this provides a way of seeing if the input you sent has been processed in that plan.