code: public SendMessageResult sendSingleTextByAdmin(String targetId, String fromId, MessageBody body)
              throws APIConnectionException, APIRequestException {
          return sendMessage(_sendVersion, "single", targetId, "admin",fromId, MessageType.TEXT, body);
      }
docs: Send single text message by admin
  @param targetId target user's id
  @param fromId sender's id
  @param body message body, include text and extra(if needed).
  @return return msg_id
  @throws APIConnectionException connect exception
  @throws APIRequestException request exception