> ## Documentation Index
> Fetch the complete documentation index at: https://docs.smartbills.io/llms.txt
> Use this file to discover all available pages before exploring further.

# .NET SDK Overview

> Official Smartbills .NET SDK for integrating invoicing, billing, and file management into your .NET applications

## Introduction

The Smartbills .NET SDK (`Smartbills.SDK`) provides a strongly-typed C# client for the Smartbills API. It is designed for server-side .NET applications and covers invoicing, file management, and billing operations.

<Info>
  The .NET SDK currently supports **InvoiceClient**, **FileClient**, and **BillingClient**. Additional service clients (expenses, vendors, reports) will be added in future releases. For broader coverage today, consider the [JavaScript SDK](/sdks/javascript/overview) or [Python SDK](/sdks/python/overview).
</Info>

## Features

| Feature                  | Description                                                          |
| ------------------------ | -------------------------------------------------------------------- |
| **Strongly Typed**       | Full C# type definitions for all requests and responses              |
| **Async/Await**          | All methods return `Task<T>` with full `CancellationToken` support   |
| **Pagination**           | Built-in `SBList<T>` response type with pagination metadata          |
| **Configurable**         | Per-request option overrides via `SBRequestOptions`                  |
| **Invoice Lifecycle**    | Create, send, void, and summarize invoices                           |
| **File Operations**      | Retrieve and update files via the Smartbills file service            |
| **Billing**              | Checkout sessions, customer management, and payment methods          |
| **Dependency Injection** | First-class ASP.NET Core integration via `Smartbills.SDK.AspNetCore` |

## Quick Start

### Install the package

```bash theme={null}
dotnet add package Smartbills.SDK
```

### Initialize the client

```csharp theme={null}
using Smartbills.SDK;

var client = new SmartbillsClient(new SmartbillsClientOptions
{
    AccessToken = "YOUR_API_KEY",
    BusinessId = 123
});
```

### Create and send an invoice

```csharp theme={null}
// Create an invoice
var invoice = await client.Invoices.CreateAsync(new InvoiceCreateRequest
{
    CustomerId = 456,
    Items = new List<InvoiceItemRequest>
    {
        new() { Description = "Consulting services", Quantity = 10, UnitPrice = 150.00m }
    },
    DueDate = DateTime.UtcNow.AddDays(30)
});

// Send it to the customer
var sent = await client.Invoices.SendAsync(invoice.Id);
```

## Architecture

The SDK follows a service-client pattern. Each domain area is accessed through a dedicated client property on the main `SmartbillsClient` instance:

```
SmartbillsClient
  |-- Invoices   (InvoiceClient)
  |-- Files      (FileClient)
  |-- Billing    (BillingClient)
       |-- CheckoutSessions
       |-- Customers
       |-- PaymentMethods
```

All methods use `long` for resource IDs and are fully asynchronous, returning `Task<T>`. Every method signature includes optional `SBRequestOptions` and `CancellationToken` parameters for per-request configuration and cooperative cancellation.

## Available Services

<CardGroup cols={2}>
  <Card title="InvoiceClient" icon="file-invoice" href="/sdks/dotnet/usage#invoiceclient">
    Full CRUD, send, void, and summary for invoices
  </Card>

  <Card title="FileClient" icon="file" href="/sdks/dotnet/usage#fileclient">
    Retrieve and update files via the Smartbills file service
  </Card>

  <Card title="BillingClient" icon="credit-card" href="/sdks/dotnet/usage#billingclient">
    Checkout sessions, customers, and payment methods
  </Card>
</CardGroup>

## Requirements

| Requirement | Minimum Version |
| ----------- | --------------- |
| .NET        | 6.0 or later    |
| C#          | 10.0 or later   |
| NuGet       | Latest          |

## Next Steps

<Card title="Installation" icon="download" href="/sdks/dotnet/installation">
  Detailed installation and configuration instructions
</Card>

<Card title="Usage Guide" icon="book" href="/sdks/dotnet/usage">
  Complete API reference for all service clients
</Card>