//return all purchase Order list
        public List <PurchaseOrder> GetAllPurchaseOrder(XeroCoreApi private_app_api)
        {
            List <PurchaseOrder> polist = private_app_api.PurchaseOrders.Find().ToList();

            foreach (var purchase in polist)
            {
                Xero.Api.Core.File.BinaryFile pdfFile = private_app_api.PdfFiles.Get(Xero.Api.Core.Model.Types.PdfEndpointType.PurchaseOrders, purchase.Id);
                string _path = System.IO.Path.Combine(Server.MapPath("~/Pdf/Purchase"), purchase.Id + ".pdf");
                pdfFile.Save(_path);
            }
            return(polist);
        }
        //return all invoice list
        public List <Invoice> GetAllInvoiceBill(XeroCoreApi private_app_api)
        {
            List <Invoice> invoicelist = private_app_api.Invoices.Find().ToList();

            foreach (var invoice in invoicelist)
            {
                //Guid invoiceId = invoice.Id;
                //Invoice invoice = private_app_api.Invoices.Find(invoiceId);
                Xero.Api.Core.File.BinaryFile pdfFile = private_app_api.PdfFiles.Get(Xero.Api.Core.Model.Types.PdfEndpointType.Invoices, invoice.Id);
                string _path = System.IO.Path.Combine(Server.MapPath("~/Pdf/Invoice"), invoice.Id + ".pdf");
                pdfFile.Save(_path);
            }

            return(invoicelist);
        }