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

# Set Up Referral Tracking

> Pass a referral code through install, read it in your app, and record the referral

Linkrunner carries a referral code from a clicked link through install. Your app reads the code from the `deeplink` returned by `getAttributionData()` and sends it to your backend.

Your app is responsible for creating referral codes, validating them, and applying rewards.

## Before you start

* [Configure a Linkrunner subdomain](/features/subdomain-setup), such as `get.example.com`.
* [Set up deep linking](/features/deep-linking-setup) for your app.
* Choose one query parameter name, such as `referrer`, and use it consistently.

## 1. Create a referral link

Add the referring user's code or ID to your Linkrunner subdomain:

```text theme={null}
https://get.example.com?referrer=user_123
```

You can include an app destination in the same link:

```text theme={null}
https://get.example.com/product/987?referrer=user_123
```

Generate the link in your app or backend when a user opens your referral or invite screen. URL-encode the value before adding it to the link.

<Note>
  You do not need to create a campaign to pass a referral code. Direct subdomain links do not appear in campaign reporting.
</Note>

## 2. Share the link

Let the referring user share the complete link. Keep the `referrer` parameter intact through any redirect or URL shortener.

When the recipient opens the link, Linkrunner sends them to the app or store. After install, the original URL is available in `getAttributionData()`:

```json theme={null}
{
  "deeplink": "https://get.example.com?referrer=user_123"
}
```

## 3. Read the referral code

Call `getAttributionData()` after the Linkrunner SDK is initialized. Parse the returned `deeplink` and read the `referrer` query parameter.

<Tabs>
  <Tab title="Android">
    ```kotlin theme={null}
    val referralCode = attributionData.deeplink
        ?.let { Uri.parse(it).getQueryParameter("referrer") }
    ```

    [Get attribution data on Android](/sdk/android#getting-attribution-data)
  </Tab>

  <Tab title="iOS">
    ```swift theme={null}
    let referralCode = URLComponents(string: deeplink)?
        .queryItems?
        .first(where: { $0.name == "referrer" })?
        .value
    ```

    [Get attribution data on iOS](/sdk/ios#getting-attribution-data)
  </Tab>

  <Tab title="React Native">
    ```javascript theme={null}
    const referralCode = new URL(attributionData.deeplink)
      .searchParams.get("referrer");
    ```

    [Get attribution data in React Native](/sdk/react-native#getting-attribution-data)
  </Tab>

  <Tab title="Flutter">
    ```dart theme={null}
    final referralCode = Uri.parse(attributionData.deeplink!)
        .queryParameters['referrer'];
    ```

    [Get attribution data in Flutter](/sdk/flutter#getting-attribution-data)
  </Tab>
</Tabs>

Store the code until the recipient signs up or completes the event that qualifies the referral.

## 4. Record the referral

Send the referral code and the recipient's user ID to your backend. Validate the relationship and record it before applying a reward.

At a minimum, reject:

* Invalid or expired codes
* Self-referrals
* A recipient using more than one referral code
* The same qualifying event being rewarded twice

<Tip>
  Validate referrals and grant rewards on your backend. Do not trust a referral code submitted only by the client.
</Tip>

## Add campaign reporting

If you also need click and install reporting in Linkrunner, append the referral parameter to a generated campaign link instead of using the subdomain directly.

```text theme={null}
https://get.example.com/AbCdEf?referrer=user_123
```

See [Deep Link Management](/features/deep-link-management) for the campaign setup and parameter precedence rules.

## Testing

1. Create a referral link with a test code.
2. Uninstall the app from a real device.
3. Open the referral link, then install and open the app.
4. Confirm that `getAttributionData()` returns the link in `deeplink`.
5. Confirm that your app extracts the referral code.
6. Sign up and confirm that your backend records the correct referrer and recipient.

<Warning>
  Deferred attribution is stored from the first install. Uninstall the app before repeating a test with a different referral code.
</Warning>

## Troubleshooting

**`deeplink` is null.** Confirm that the SDK was initialized before calling `getAttributionData()` and that the app was installed through the referral link.

**The referral parameter is missing.** Open the final URL before the store redirect and confirm that no redirect or URL shortener removed it.

**The previous referral code is returned.** Uninstall the app before testing another link. Attribution data is cached from the first install.

**The referral is not visible in campaign reporting.** Direct subdomain links are not associated with a campaign. Use a generated campaign link when you need dashboard reporting.

**The code is present but no referral is recorded.** Check the app-to-backend request and your referral validation logic. Linkrunner forwards the code but does not apply referral rules or rewards.

**Need help?** Contact [support@linkrunner.io](mailto:support@linkrunner.io)