The requested message is already being modified in this service instance concurrently with another API request. The last request will be rejected to avoid inconsistent state.
Possible Causes
You might be submitting multiple concurrent requests to modify a message or its attributes with the same SID in the service instance.
Possible Solutions
Implement an operation retrier and repeat the failed API requests after an interval of time, using an exponential backoff algorithm.
Review your application logic that caused the race condition when modifying a message. Perhaps the conflicting operations are happening in a loop that could be avoided.
Serialize your API requests that modify conversation messages. Wait until the original request completes and returns an API response, before sending any successive conversation requests.