> For the complete documentation index, see [llms.txt](https://docs.ecommerce.seb.ee/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ecommerce.seb.ee/integration/api-client-sdk/quickstarts/c-.net.md).

# C# / .NET

Set up the C# / .NET SDK, initiate a sandbox payment, and configure client adapters.

## Prerequisites

* .NET 8 SDK.
* Sandbox API credentials: **client ID** and **client secret**, plus your **participant ID** and **shop agreement ID**. Register and generate these yourself at the **Merchant Portal**: <https://merchantportal.ecommerce.sebgroup.com>.
* The SDK **distribution ZIP**, downloaded from this documentation site.

## Install

Download `egw-csharp-sdk-<version>.zip` and its matching `.sha256` file, verify the download, then unzip it next to your project:

```bash
sha256sum -c egw-csharp-sdk-<version>.zip.sha256

unzip egw-csharp-sdk-<version>.zip -d egw-sdk
```

That gives you `Egw.Sdk.<version>.nupkg` and its matching `Egw.Sdk.<version>.snupkg` (debug symbols), alongside a `README.txt` and a `SHA256SUMS` manifest. Add that directory as a package source and install from it:

```bash
dotnet add package Egw.Sdk --version <version> --source ./egw-sdk
```

Or register the source once in `nuget.config` instead of passing `--source` every time:

```xml
<configuration>
  <packageSources>
    <add key="egw-local" value="./egw-sdk" />
  </packageSources>
</configuration>
```

The package name is `Egw.Sdk`, and its runtime dependencies are `jose-jwt` and `System.Text.Json`. NuGet restores those from your normal package sources, so the install needs network access to them.

## Create a client and make your first call

In this example, the credentials are retrieved from environment variables — never commit or log real credentials. All operations are **async-only**.

```csharp
using Egw.Sdk.Application;
using Egw.Sdk.Application.Bootstrap;
using Egw.Sdk.Application.Dto;

using EgwClient client = new DefaultEgwClientFactory()
    .ConnectingTo("https://sandbox.api.ecommerce.sebgroup.com")
    .TokenEndpoint("https://api.ecommerce.sebgroup.com/auth/realms/participants-seb/protocol/openid-connect/token")
    .AuthorizingAs(
        Environment.GetEnvironmentVariable("EGW_CLIENT_ID")!,
        Environment.GetEnvironmentVariable("EGW_CLIENT_SECRET")!)
    .EncryptingWith("https://checkout.ecommerce.sebgroup.com/api/keys/card-encryption.jwk") // required for card sessions
    .CreateEgwClient();

InitiatePaymentResponse response = await client.Payments().InitiateCitPaymentAsync(
    Guid.NewGuid(),
    b => b.Channel(CitPaymentChannel.BROWSER)
          .InstructedAmount(a => a.VarAmount("100.00").Currency("EUR"))
          .OrderNumber("ORD-001")
          .ParticipantId(Environment.GetEnvironmentVariable("EGW_PARTICIPANT_ID")!)
          .ShopAgreementId(Environment.GetEnvironmentVariable("EGW_SHOP_AGREEMENT_ID")!)
          .ShopRedirectUrl("https://shop.example.com/return")
          .Description("First sandbox payment"));

Console.WriteLine($"Payment created: {response.PaymentId}");
```

Notes:

* `TokenEndpoint(...)` is **required**; omitting it fails at `CreateEgwClient()` with `EgwBootstrapException`.
* `EncryptingWith(...)` is optional, but without it any card-encryption call throws — configure it if you use card checkout sessions.
* The amount setter is `VarAmount(...)` (the JSON field is still `amount`); amounts are **decimal strings**, currencies ISO 4217 alpha-3. For test cards and magic values, see [Sandbox test data](/guides/sandbox.md).
* `EgwClient` is `IDisposable`; disposing stops the webhook listener if one was started. The client is safe to share across requests.

## Customizing the client

* Using `ConnectingWith()`, you may supply your own HTTP client implementation.
* Logging: implement `IEgwLoggerProvider`; the default logger is silent. See [Security mechanics](/integration/api-client-sdk/guides/security-mechanics.md#logging).
* Webhooks: `ListeningOn(uri)` + `client.Notifications().ReceiveNotifications(...)` — see [Security mechanics](/integration/api-client-sdk/guides/security-mechanics.md#webhook-notifications).
* See [Overriding SDK adapters](/integration/api-client-sdk/guides/overriding-sdk-adapters.md) for a full walkthrough of replacing adapters application-wide.

## Next steps

* [Security mechanics](/integration/api-client-sdk/guides/security-mechanics.md) — card encryption for card checkout sessions, webhooks.
* [Error handling](/integration/api-client-sdk/guides/error-handling.md) — the exception hierarchy and retry guidance.


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