کار با موجودیت صورتحساب

/// <summary>
/// صورتحساب سامانهٔ مؤدیان
/// </summary>
public class IntamediaInvoice
{
    /// <summary>
    /// Id
    /// </summary>
    public Guid Id { get; set; }

    /// <summary>
    /// Workspace Id
    /// </summary>
    public Guid WorkspaceId { get; set; }
    
    /// <summary>
    /// وضعیت
    /// </summary>
    public IntamediaInvoiceStatus InvoiceStatus { get; set; }    

// اعضای دیگر کلاس برای سادگی در این کد نمونه نیامده است
}

return new Dictionary<IntamediaInvoiceStatus, string>
{
    { IntamediaInvoiceStatus.Draft, "ارسال نشده"},
    { IntamediaInvoiceStatus.Queued , "در صف ارسال"},
    { IntamediaInvoiceStatus.Sending , "در دست ارسال"},
    { IntamediaInvoiceStatus.Inquirying , "در دست استعلام"},
    { IntamediaInvoiceStatus.Errornous , "دارای خطا"},
    { IntamediaInvoiceStatus.Succeeded , "ارسال موفق"},
    { IntamediaInvoiceStatus.Edited , "ویرایش شده پس از ارسال"},
    { IntamediaInvoiceStatus.InProgress , "در حال پردازش"},
    { IntamediaInvoiceStatus.WaitingForInquiry , "در بازهٔ انتظار پیش از استعلام"},
    { IntamediaInvoiceStatus.NotFound , "NOT_FOUND"},
    { IntamediaInvoiceStatus.Unknown , "خطای ناشناخته"},
    { IntamediaInvoiceStatus.InquiryAborted , "خروج دستی از صف استعلام"},
    { IntamediaInvoiceStatus.SendFailed , "خطا در ارتباط با سامانه"},
    { IntamediaInvoiceStatus.SucceededInLastSession , "ارسال موفق (اخیر)"},
    { IntamediaInvoiceStatus.ChargeRunOut , "عدم ارسال به دلیل شارژ ناکافی"},
    { IntamediaInvoiceStatus.Timeout , "پردازش طولانی"},
    { IntamediaInvoiceStatus.NotCurrent , "غیرجاری"},
    { IntamediaInvoiceStatus.Reserved17 , "Reserved17"},
    { IntamediaInvoiceStatus.Reserved18 , "Reserved18"},
    { IntamediaInvoiceStatus.Reserved19 , "Reserved19"},
    { IntamediaInvoiceStatus.Current , "جاری"},
    { IntamediaInvoiceStatus.All , "همه"},
};

using (HttpClient httpClient = new HttpClient())
{
    await MoaddiyanSessionChecker.PrepareClientAsync(httpClient);
    var response = await httpClient.GetAsync
        (
        $"https://api.moaddiyan.com/api/invoice/{Settings.Default.WorkspaceId}?PageNumber=1&PageSize=50&status={(cmbStatus.SelectedItem as IntamediaInvoiceStatusDescriptor).IntamediaInvoiceStatus}&invoiceNumber=0"
        );
    if (response.StatusCode != HttpStatusCode.OK)
    {
        Cursor = Cursors.Default;
        Enabled = true;
        MessageBox.Show(JsonConvert.DeserializeObject<string>(await response.Content.ReadAsStringAsync()));
        return;
    }
    response.EnsureSuccessStatusCode();
    Cursor = Cursors.Default;
    Enabled = true;
    var invoices = JsonConvert.DeserializeObject<IntamediaInvoice[]>(await response.Content.ReadAsStringAsync());
    if (invoices != null)
    {
        grd.DataSource = invoices;
    }
}

var pagingMeta = JsonConvert.DeserializeObject<PaginationMetadata>(response.Headers.GetValues("paging-headers").Single());
lblPaging.Text = $"صفحهٔ {pagingMeta.currentPage} از {pagingMeta.totalPages} - تعداد کل: {pagingMeta.totalCount}";

    long invoiceNumber = 1;
    using (HttpClient httpClient = new HttpClient())
    {
        await MoaddiyanSessionChecker.PrepareClientAsync(httpClient);
        var response = await httpClient.GetAsync
            (
            $"https://api.moaddiyan.com/api/invoice/{Settings.Default.WorkspaceId}/last"
            );
        if (response.StatusCode != HttpStatusCode.OK)
        {
            MessageBox.Show(JsonConvert.DeserializeObject<string>(await response.Content.ReadAsStringAsync()));
            return;
        }
        response.EnsureSuccessStatusCode();
        var lastInvoice = JsonConvert.DeserializeObject<IntamediaInvoice>(await response.Content.ReadAsStringAsync());
        if(lastInvoice != null)
        {
            invoiceNumber = lastInvoice.InvoiceNumber + 1;
        }
    }

            var measurementUnit = IntamediaMeasurementUnit.Units.Where(u => u.Name == "عدد").Single(); //واحد اقلام صورتحساب

            IntamediaInvoice invoice = new IntamediaInvoice()
            {
                WorkspaceId = Settings.Default.WorkspaceId, //شرکت
                InvoiceNumber = invoiceNumber, //شماره یا سریال داخلی صورتحساب
                DateTime = DateTime.Now, //تاریخ و زمان صدور صورتحساب
                InvoiceSubject = IntamediaInvoiceSubject.Main,// موضوع صورتحساب
                InvoiceType = IntamediaInvoiceType.Type2, //نوع صورتحساب
                InvoicePattern = IntamediaInvoicePattern.Pattern1NormalSales,//الگوی صورتحساب
                RecalculateSums = true,//جمع‌ها به طور خودکار حساب شود
                AdditionalNote = "ایجاد شده با API",
                Items =
                [
                    new IntamediaInvoiceItem()
                    {
                        StuffId = "2900750000016",//شناسهٔ کالا / خدمت
                        Description = "نرم‌افزار تدبیر",//شرح
                        Amount = 2,//تعداد یا مقدار
                        MeasurementUnitCode = measurementUnit.Code,
                        MeasurementUnitName = measurementUnit.Name,
                        UnitPrice = 10_000_000,//مبلغ واحد به ریال
                        Discount = 0, //تخفیف سطر به ریال
                        ValueAddedTaxRateInPercent = 10,//درصد مالیات بر ارزش افزوده
                    },
                    new IntamediaInvoiceItem()
                    {
                        StuffId = "2330002811587",
                        Description = "خدمات پشتیبانی",
                        Amount = 3,
                        MeasurementUnitCode = measurementUnit.Code,
                        MeasurementUnitName = measurementUnit.Name,
                        UnitPrice = 2_000_000,
                        Discount = 500_000,
                        ValueAddedTaxRateInPercent = 10,
                    },
                ]
            };

            using (HttpClient httpClient = new HttpClient())
            {
                await MoaddiyanSessionChecker.PrepareClientAsync(httpClient);
                var response = await httpClient.PostAsync
                    (
                    $"https://api.moaddiyan.com/api/invoice/{Settings.Default.WorkspaceId}",
                     new StringContent(JsonConvert.SerializeObject(invoice), Encoding.UTF8, "application/json")
                    );
                if (response.StatusCode != HttpStatusCode.OK)
                {
                    MessageBox.Show(JsonConvert.DeserializeObject<string>(await response.Content.ReadAsStringAsync()));
                    return;
                }
                response.EnsureSuccessStatusCode();
                var newInvoice = JsonConvert.DeserializeObject<IntamediaInvoice>(await response.Content.ReadAsStringAsync());
                MessageBox.Show(newInvoice.TaxId);
            }