### Install ZUGFeRD-CSharp Libraries

Source: https://context7.com/stephanstapel/zugferd-csharp/llms.txt

Install the core ZUGFeRD-csharp library and the optional PDF/A-3 integration package using the .NET CLI.

```bash
# Install core library via NuGet
dotnet add package ZUGFeRD-csharp

# Optional: PDF/A-3 integration
dotnet add package ZUGFeRD.PDF-csharp
```

--------------------------------

### Document-Level Discounts and Surcharges in C#

Source: https://context7.com/stephanstapel/zugferd-csharp/llms.txt

Adds document-level allowances (discounts) and charges (surcharges). Includes examples for early payment discounts, freight surcharges, and logistics service charges.

```csharp
// 5% early-payment discount on the net total
desc.AddTradeAllowance(
    basisAmount: 1000.00m,
    currency: CurrencyCodes.EUR,
    actualAmount: 50.00m,
    chargePercentage: 5m,
    reason: "Early payment discount",
    taxTypeCode: TaxTypes.VAT,
    taxCategoryCode: TaxCategoryCodes.S,
    taxPercent: 19m,
    reasonCode: AllowanceReasonCodes.Discount
);

// Freight surcharge
desc.AddTradeCharge(
    basisAmount: null,
    currency: CurrencyCodes.EUR,
    actualAmount: 10.00m,
    chargePercentage: null,
    reason: "Freight",
    taxTypeCode: TaxTypes.VAT,
    taxCategoryCode: TaxCategoryCodes.S,
    taxPercent: 19m
);

// Logistics service charge (ZUGFeRD/Factur-X only, not XRechnung)
desc.AddLogisticsServiceCharge(5.80m, "Shipping costs", TaxTypes.VAT, TaxCategoryCodes.S, 7m);
```

--------------------------------

### Create a Basic ZUGFeRD Invoice Descriptor

Source: https://github.com/stephanstapel/zugferd-csharp/blob/master/docs/getting-started.md

Initializes an InvoiceDescriptor with essential details like invoice ID, date, currency, and reference. This is the starting point for building any ZUGFeRD invoice.

```csharp
InvoiceDescriptor desc = InvoiceDescriptor.CreateInvoice("471102", new DateTime(2013, 6, 5), CurrencyCodes.EUR, "GE2020211-471102");

desc.Name = "WARENRECHNUNG";

desc.ReferenceOrderNo = "AB-312";

desc.AddNote("Rechnung gemäß Bestellung Nr. 2013-471331 vom 01.03.2013.");

desc.AddNote("Es bestehen Rabatt- und Bonusvereinbarungen.", SubjectCodes.AAK);

desc.SetBuyer("Kunden Mitte AG", "69876", "Frankfurt", "Kundenstraße 15", CountryCodes.DE, "88", new GlobalID(GlobalIDSchemeIdentifiers.GLN, "4000001123452"));

desc.AddBuyerTaxRegistration("DE234567890", TaxRegistrationSchemeID.VA);

desc.SetBuyerContact("Hans Muster");

desc.SetSeller("Lieferant GmbH", "80333", "München", "Lieferantenstraße 20", CountryCodes.DE, "88", new GlobalID(GlobalIDSchemeIdentifiers.GLN, "4000001123452"));

desc.AddSellerTaxRegistration("201/113/40209", TaxRegistrationSchemeID.FC);

desc.AddSellerTaxRegistration("DE123456789", TaxRegistrationSchemeID.VA);

desc.SetBuyerOrderReferenceDocument("2013-471331", new DateTime(2013, 03, 01));

desc.SetDeliveryNoteReferenceDocument("2013-51111", new DateTime(2013, 6, 3));

desc.ActualDeliveryDate = new DateTime(2013, 6, 3);

desc.SetTotals(202.76m, 5.80m, 14.73m, 193.83m, 21.31m, 215.14m, 50.0m, 165.14m);

desc.AddApplicableTradeTax(129.37m, 7m, TaxTypes.VAT, TaxCategoryCodes.S);

desc.AddApplicableTradeTax(64.46m, 19m, TaxTypes.VAT, TaxCategoryCodes.S);

desc.AddLogisticsServiceCharge(5.80m, "Versandkosten", TaxTypes.VAT, TaxCategoryCodes.S, 7m);

desc.AddTradePaymentTerms("Zahlbar innerhalb 30 Tagen netto bis 04.04.2018", new DateTime(2018, 4, 4));

desc.AddTradePaymentTerms("3% Skonto innerhalb 10 Tagen bis 15.03.2018", new DateTime(2018, 3, 15), PaymentTermsType.Skonto, 30, 3m);
```

--------------------------------

### XML Schema Validation Example

Source: https://github.com/stephanstapel/zugferd-csharp/blob/master/documentation/zugferd240en/Examples/3. EN16931/EN16931_Reisekostenabrechnung/EN16931_Reisekostenabrechnung_analyzed-content.html

Demonstrates how to validate an XML document against a specific schema. This is crucial for ensuring data integrity and compliance.

```csharp
XmlSchemaSet schemaSet = new XmlSchemaSet();
schemaSet.Add("http://www.w3.org/2001/XMLSchema", "XSD_Schema.xsd");

XmlReaderSettings settings = new XmlReaderSettings();
settings.ValidationType = ValidationType.Schema;
settings.Schemas = schemaSet;
settings.ValidationEventHandler += new ValidationEventHandler(ValidationCallBack);

XmlReader reader = XmlReader.Create("XML_File.xml", settings);

while (reader.Read())
{
}

reader.Close();
```

--------------------------------

### Validate Invoice Monetary Summation

Source: https://context7.com/stephanstapel/zugferd-csharp/llms.txt

Validate the monetary summation of an invoice and get a structured result. Use ValidateAndPrint to also output to a file.

```csharp
ValidationResult result = InvoiceValidator.Validate(desc, ZUGFeRDVersion.Version23);

if (result.IsValid)
{
    Console.WriteLine("Invoice is valid.");
}
else
{
    Console.WriteLine("Invoice validation FAILED:");
    foreach (string msg in result.Messages)
    {
        Console.WriteLine($"  {msg}");
    }
}
```

```csharp
// Validate and print to console and optionally to a file
InvoiceValidator.ValidateAndPrint(desc, ZUGFeRDVersion.Version23, filename: "validation-report.txt");
```