# 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 %}