code: @Override
      public Response attachStatement(String CorpNum, MgtKeyType KeyType, String MgtKey,
                                      int SubItemCode, String SubMgtKey) throws PopbillException {
  
          DocRequest request = new DocRequest();
          request.ItemCode = Integer.toString(SubItemCode);
          request.MgtKey = SubMgtKey;
  
          String PostData = toJsonString(request);
  
          return httppost("/Taxinvoice/" + KeyType.name() + "/" + MgtKey + "/AttachStmt",
                  CorpNum, PostData, null, "", Response.class);
      }
docs: /*
  
  /*
  (non-Javadoc)
  @see com.popbill.api.TaxinvoiceService#attachStatement(java.lang.String, com.popbill.api.taxinvoice.MgtKeyType, java.lang.String, int, java.lang.String)