namespace Export
{
    public class XeroExport: ApiWrapper
    {
        public void ExcelExport()
        {
            DateTime startDate = DateTime.ParseExact(ConfigurationManager.AppSettings["PeriodStart"], "yyyy-MM-dd HH:mm:ss,fff", System.Globalization.CultureInfo.InvariantCulture);
            DateTime endDate = DateTime.ParseExact(ConfigurationManager.AppSettings["PeriodEnd"], "yyyy-MM-dd HH:mm:ss,fff", System.Globalization.CultureInfo.InvariantCulture);
            Call_BalanceSheet(startDate, endDate);
        }
        private List<InvoiceTableRow> converZInvouice(Invoice invoice)
        {
        }
        private String convertInvoiceToString(Invoice invoice)
        {
        }
        private void saveInvoices(string filename, List<Invoice> invoices)
        {
        }
        private void GetInvoices()
        {
        }
        private int GetTotalInvoiceCount()
        {
        }
        private int GetTotalContactCount()
        {
        }
        private int GetTotalJournalCount()
        {
        }
        public int CheckReportStatus(string ReportName)
        {
            ...  
            return ReportStatus;
        }
        private void Call_BalanceSheet(DateTime periodStart, DateTime periodEnd)
        {
            int reportStatus = CheckReportStatus("Balance Sheet");
            if (reportStatus == 1)
            {
                 ...
                 Insert_BalanceSheet(monthStartDate, monthEndDate, reportDate);
                 ...
            }
        }
        private void Insert_BalanceSheet(DateTime periodStart, DateTime periodEnd, DateTime runDate)
        {
            ...   
            var pal = Api.Reports.BalanceSheet(periodStart, null, null, false, null, null, null);
        }
    }
}

using System;
using System.Configuration;
using System.Data.SqlClient;
using System.Data;
using Xero.Api.Example.MVC.Helpers;

namespace Export
{

    public class BalanceSheet
    {
        private void Call_BalanceSheet(DateTime periodStart, DateTime periodEnd)
        {
            int reportStatus = CheckReportStatus("Balance Sheet");
            if (reportStatus == 1)
            {
               ... 
               Insert_BalanceSheet(monthStartDate, monthEndDate, reportDate);
            }
        }
        private void Insert_BalanceSheet(DateTime periodStart, DateTime periodEnd, DateTime runDate)
        {
             ....
             var pal = Api.Reports.BalanceSheet(periodStart, null, null, false, null, null, null);
        }
    }

}

            
var balancesheet = new BalanceSheet();
balancesheet.Call_BalanceSheet(startDate, endDate);

var checkReportStatus = new XeroExport();        
int reportStatus = checkReportStatus.CheckReportStatus("Balance Sheet");

using System;
using System.Configuration;
using System.Data.SqlClient;
using System.Data;
using System.Collections.Generic;
using Xero.Api.Core.Model;
using Xero.Api.Core;
using Xero.Api.Payroll.Australia.Model;
using System.Linq;

public class XeroExport: ApiWrapper

public class XeroExport: ApiWrapper

   public class ApiWrapper
    {
        public ApiWrapper()
        {
            System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12;
        }

        private IXeroCoreApi _api;
        protected IXeroCoreApi Api
        {
            get { return _api ?? (_api = CreateCoreApi()); }
        }

        private static IXeroCoreApi CreateCoreApi()
        {
            return new Xero.Api.Example.Applications.Private.Core
            {
                UserAgent = "Xero Api - Integration tests"
            };
        }

    }