Can you please provide some additional information about above error. By error description, its clear that the request sent from api failed to process at your OMS. I saw this error in logs at around 09:15:19 while order Modify.
Need to know, 1) My understanding of the error is correct? 2) It had come today due to OMS issue or any network issue? OMS down? or OMS not reachable? 3) What are the chances of it reoccurring. Is it serious or minor issue? 4) How do i handle it. A try catch and retry mechanism should be used for this error... ? Or the retry will add more burden on your system and/or OMS?