docs: @Override
  	public Response issue(String CorpNum, String MgtKey, String Memo,
  			String UserID) throws PopbillException {
  		if (MgtKey == null || MgtKey.isEmpty())
  			throw new PopbillException(-99999999, "관리번호가 입력되지 않았습니다.");
  
  		String PostData = toJsonString(new MemoRequest(Memo));
  
  		return httppost("/Cashbill/" + MgtKey, CorpNum, PostData,
  				UserID, "ISSUE", Response.class);
  	}