code: public void submitConversion(ConversionRequest.Type type,
                                   String messageId,
                                   boolean delivered,
                                   Date timestamp) throws IOException, NexmoClientException {
          this.conversionEndpoint.submitConversion(new ConversionRequest(type, messageId, delivered, timestamp));
      }
docs: Submit a request to the Conversion API indicating whether or not a message was delivered.
  
  @param type      The {@link ConversionRequest.Type} type of com.nexmo.client.conversion.
  @param messageId The id of the message that was sent.
  @param delivered A boolean indicating whether or not it was delivered.
  @param timestamp A timestamp of when it was known to be delivered.
  @throws IOException          if a network error occurred contacting the Nexmo Conversion API.
  @throws NexmoClientException if there was a problem with the Nexmo request or response objects.