This error code is returned by the /Summary API when a completed summary is requested and it doesn't exist.
The call SID for the call is valid, but the call summarization process was not complete at the time of the request. Summarization takes 30 minutes to complete.
To see results immediately, use the ProcessingState=partial query parameter, which will return a 200, but the response will contain only a partial or incomplete information until the summarization is completed.