Provided that you are using the RingCentral Java SDK, you can read the transcript file as shown below.

public void read_message_store_voicemail() throws RestException, IOException{

        ListMessagesParameters parameters = new ListMessagesParameters();

        parameters.messageType = new String[] {"VoiceMail"};

        

        var response = restClient.restapi().account().extension().messagestore().list(parameters);

        for (GetMessageInfoResponse record : response.records)

        {

            if (record.attachments != null)

            {

                for (var attachment : record.attachments)

                {

                    var fileName = "./src/test/resources/" + record.attachments[0].id + "_voicemail.txt";

                    if (attachment.type.equals("AudioTranscription"))

                   {

                    var res = restClient.restapi().account().extension().messagestore(record.id).content(attachment.id).get();

                    Path path = Paths.get(fileName);

                    Files.write(path, res);

                    }

                }

            }

        }

    }

Hope this helps.