> For the complete documentation index, see [llms.txt](https://documentation.pushly.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://documentation.pushly.com/integration/implementation-steps/react-native/sdk-react-native/identity-synchronization.md).

# Identity Synchronization

## Setting the Subscriber's External ID

Providing a unique User ID for your subscriber allows you to later interact with that subscriber via the API.

Once a subscriber's external ID has been set you may work with our team to set up bi-directional automated data syncs. The following use cases are common ways that publishers use the external ID via server-to-server requests:

* Sending notifications to individual subscribers programmatically
* Processing unsubscribe requests
* Adding and removing profile attributes and events to subscribers

{% tabs %}
{% tab title="React" %}

```tsx
PushSDK.UserProfile.setExternalId("external-id");
```

{% endtab %}
{% endtabs %}

You can also check to see if the subscriber is already tagged with an External ID:

{% tabs %}
{% tab title="React" %}

```tsx
const currentExternalId = await PushSDK.UserProfile.getExternalId();
```

{% endtab %}
{% endtabs %}


---

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