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

# Server SDK — Installation

> Install @unseen_fi/sdk and instantiate UnseenClient for server-side payments and webhooks helpers.

You now know how a payment [evolves over time](/concepts/payment-lifecycle); this SDK is **how your backend creates and verifies those sessions programmatically**.

## Package

The server SDK is published as **`@unseen_fi/sdk`**.

<CodeGroup>
  ```bash npm theme={null}
  npm install @unseen_fi/sdk
  ```

  ```bash pnpm theme={null}
  pnpm add @unseen_fi/sdk
  ```

  ```bash yarn theme={null}
  yarn add @unseen_fi/sdk
  ```
</CodeGroup>

Requires a modern Node runtime with global `fetch` (Node 18+).

## Create a client

```ts theme={null}
import { UnseenClient } from "@unseen_fi/sdk";

const unseen = new UnseenClient({
  apiKey: process.env.UNSEEN_API_KEY!,
  network: "mainnet", // or "devnet" — align hosts per /concepts/environments
});

// Optionally override the API host entirely:
// new UnseenClient({ apiKey, baseUrl: "https://staging.example.com" })
```

See [Payments API](/sdk/server/client-payments) for `payments.*` methods and [Webhooks verification](/sdk/server/webhooks-verify) for `unseen.webhooks.verify`.

**Next:** [Client & payments](/sdk/server/client-payments)