SyntaxError: Unexpected non-whitespace character after JSON at position 221 (line 1 column 222) by ajax in asp.net

When form load at that time I am calling .asmx.cs page via Ajax at that time getting error

SyntaxError: Unexpected non-whitespace character after JSON at position 221 (line 1 column 222)

Here is my Ajax code:

window.addEventListener('load', function () {                 
    var date1 = document.getElementById('<%= dtp_from.ClientID %>').value || new Date().toISOString().split('T')[0]; // Default to today if empty
    var date2 = document.getElementById('<%= dtp_to.ClientID %>').value || new Date().toISOString().split('T')[0];
    var dataToSend = JSON.stringify({ fromDate: date1, toDate: date2 });            
    $.ajax({
        type: "POST",
        url: "FillGridMethod.asmx/CashBookList",                    
        async: true,
        data: dataToSend,
        dataType: "json",
        contentType: "application/json; charset=utf-8",
        success: function (data) {
            alert();
            var datatableVariable = $('#gv_Datatable').DataTable({
                dom: 'Bfrtip',
                buttons: [
                    'pdf', 'print', 'excel'
                ],
                "bDestroy": true,
                "paging": true,
                "searching": true,
                "ordering": true,
                "info": true,
                "autoWidth": false,
                "responsive": true,
                data: data,
                columns: [
                    {
                        className: 'dt-control',
                        orderable: false,
                        data: null,
                        defaultContent: ''
                    },
                    { 'data': 'Id', visible: false },
                    {
                        'data': 'cashbookdate', 'render': function (date) {
                            var date = new Date(parseInt(date.substr(6)));
                            var month = date.getMonth() + 1;
                            return date.getDate() + "/" + month + "/" + date.getFullYear();
                        }
                    },
                    { 'data': 'cashbookaccname' },
                    { 'data': 'cashbookreceipt' },
                    { 'data': 'cashbookpayment' },
                    { 'data': 'Balance' },
                    {
                        "render": function (data, type, row) { return "<a href='#' class='btn btn-success' onclick=DeleteCustomer('" + row.Id + "');>View</>"; }
                    },
                    {
                        "render": function (data, row) { return "<a href='#' class='btn btn-danger'>Delete</a>"; }
                    }],
                footerCallback: function (row, data, start, end, display) {
                    var api = this.api();
                    // Calculate the total for the filtered data
                    var total = api.column(4, { page: 'current' }).data().reduce(function (a, b) {
                        return parseFloat(a) + parseFloat(b);
                    }, 0);
                    // Update the footer with the total
                    $(api.column(4).footer()).html(total.toFixed(2));

                    // Calculate the total for the filtered data
                    var total = api.column(5, { page: 'current' }).data().reduce(function (a, b) {
                        return parseFloat(a) + parseFloat(b);
                    }, 0);
                    // Update the footer with the total
                    $(api.column(5).footer()).html(total.toFixed(2));
                }
            });                                                
            $('.showHideDatatable').on('click', function () {
                var tableColumn = datatableVariable.column($(this).attr('data-columnindex'));
                tableColumn.visible(!tableColumn.visible());
            });
            // Add event listener for opening and closing details
            datatableVariable.on('click', 'td.dt-control', function (e) {
                let tr = e.target.closest('tr');
                let row = datatableVariable.row(tr);

                if (row.child.isShown()) {
                    // This row is already open - close it
                    row.child.hide();
                }
                else {
                    // Open this row
                    if (row.data()) {
                        // Open this row
                        row.child(format(row.data())).show();
                    } else {
                        console.error('Row data is undefined');
                    }
                }
            });
        },
        error: function (xhr, status, error) {              
            alert("AJAX Error!\nStatus: " + status + "\nMessage: " + error + "\nResponse: " + xhr.responseText);
        },
        complete: function () {
            // Hide the loading indicator
            $('#loadingOverlay').hide();
        }
    });
});

This is my .asmx.cs code:

[WebMethod(enableSession: true)]
public void CashBookList(string fromDate, string toDate)
{
    if(HttpContext.Current.Session["BranchId"].ToString() == null) {
        Server.Transfer("Index.aspx");
        return;
    }            

    var cashBook = new List<CashBookModel>();
    string constr = cn.ConnectionString;

    using (SqlConnection con = new SqlConnection(constr))
    {
        qryFillGrid = " select cashbookid, cashbookdate, cashbookaccname, Ledger.Name as OthAcc, cashbookdescription, cashbookreceipt, cashbookpayment, Balance " + System.Environment.NewLine;
        qryFillGrid += " from tbl_cashbook cash Left Outer Join tbl_Ledger ledger on ledger.Ledger_ID = cash.OtherAccountId " + System.Environment.NewLine;
        qryFillGrid += " where cash.BranchID = " + HttpContext.Current.Session["BranchID"] + " " + System.Environment.NewLine;

        if (HttpContext.Current.Session["AccountMode"].ToString() != "ALL")
        {
            qryFillGrid += " and AccountMode = '" + HttpContext.Current.Session["AccountMode"].ToString() + "' " + System.Environment.NewLine;
        }

        qryFillGrid += " and convert(varchar(10), convert(datetime, cashbookdate,105),112) >= '" + Convert.ToDateTime(fromDate).Date.ToString("yyyyMMdd") + "' " + System.Environment.NewLine;
        qryFillGrid += " and convert(varchar(10), convert(datetime, cashbookdate,105),112) <= '" + Convert.ToDateTime(toDate).Date.ToString("yyyyMMdd") + "' " + System.Environment.NewLine;
        qryFillGrid += " order by cashbookdate, cashbookid desc " + System.Environment.NewLine;

        var cmd = new SqlCommand(qryFillGrid, con);
        cmd.CommandTimeout = 120; // Timeout in seconds

        con.Open();
        var dr = cmd.ExecuteReader();                

        while (dr.Read())
        {
            var cashBookModel = new CashBookModel
            {
                Id = Convert.ToInt32(dr[0]),
                cashbookdate = Convert.ToDateTime(dr[1]),
                cashbookaccname = dr[2].ToString(),
                OtherAccount = dr[3].ToString(),
                cashbookdescription = dr[4].ToString(),
                cashbookreceipt = Convert.ToDecimal(service.IfNullThen(dr[5], 0)),
                cashbookpayment = Convert.ToDecimal(service.IfNullThen(dr[6], 0)),
                Balance = Convert.ToDecimal(service.IfNullThen(dr[7], 0))
            };
            cashBook.Add(cashBookModel);
        }                
    }

    var js = new JavaScriptSerializer();
    Context.Response.Write(js.Serialize(cashBook));
}

Note: this error is occurring while I am calling parameter, if I remove the parameter, then it's working perfectly.

Here is the output I am getting:

State: parsererror
Error: Unexpected non-whitespace character after JSON at position 221 (line 1 column 222)
Response:
"Id": 1044,
"cashbookdate": "/Date(1741113000000)/",
"cashbookaccname": "RAJU BHAI",
"cashbookreceipt": 500.00,
"cashbookpayment": 0.00,
"cashbookdescription": "",
"Balance": 0,
"totalReceipt": 0,
"totalPayment": 0,
"OtherAccount": ""