code: public String resendFAX(String corpNum, String receiptNum, String sendNum,
  			String senderName, Receiver[] receivers, Date reserveDT,
  			String userID, String title, String requestNum) throws PopbillException {
  		
  		if(receiptNum == null)
  			throw new PopbillException(-99999999,"팩스 접수번호(receiptNum)가 입력되지 않았습니다.");
  		if (receiptNum.length() != 18)
  			throw new PopbillException(-99999999, "접수번호가 올바르지 않았습니다.");
  		
  		SendRequest request = new SendRequest();
  		
  		if (sendNum != null)
  			request.snd = sendNum;
  		
  		if ( senderName != null)
  			request.sndnm = senderName;
  		
  		if ( title != null)
  			request.title = title;
  
  		if (receivers != null) 
  			request.rcvs = receivers;
  		
  		if (reserveDT != null) 
  			request.sndDT = new SimpleDateFormat("yyyyMMddHHmmss", Locale.KOREA).format(reserveDT);
  		
  		if (requestNum != null) 
  			request.requestNum = requestNum;
  		
  		String PostData = toJsonString(request);
  		
  		ReceiptResponse response = httppost("/FAX/"+receiptNum, corpNum, PostData, userID, ReceiptResponse.class);
  		
  		return response.receiptNum;
  	}
docs: /*
  verride(non-Javadoc)
  @see com.popbill.api.FaxService#resendFAX(java.lang.String, java.lang.String, java.lang.String, java.lang.String, com.popbill.api.fax.Receiver[], java.util.Date, java.lang.String, java.lang.String, java.lang.String)