docs: @Override
  	public Response cancelReserve(String corpNum, String receiptNum,String userID)
  			throws PopbillException {
  		if (receiptNum == null)
  			throw new PopbillException(-99999999, "접수번호가 입력되지 않았습니다.");
  		if (receiptNum.length() != 18)
  			throw new PopbillException(-99999999, "접수번호가 올바르지 않았습니다.");
  
  		return httpget("/FAX/" + receiptNum + "/Cancel", corpNum, userID,
  				Response.class);
  	}