code: func (conn *BytesManualConnectionStr) SendSyncMessageToPartition(topic string, partition int32, key client.Encoder, value client.Encoder) (offset int64, err error) {
  	msg, err := conn.multiplexer.manSyncProducer.SendMsgToPartition(topic, partition, key, value)
  	if err != nil {
  		return 0, err
  	}
  	return msg.Offset, err
  }
docs: //SendSyncMessageToPartition sends a message using the sync API and default partitioner