# Add or update additional client ID

You can use the **Additional Client ID** field on the agreement details page to enter a purchase order number for billing and invoicing purposes.

When saved, this number is displayed in your invoice header. For details, see the [Invoice header](/modules-and-features/billing/understand-your-billing-documents.md#invoice-header) section in [Understand your billing documents](/modules-and-features/billing/understand-your-billing-documents.md).  If you entered a value when placing the order, the same value can also be updated.

### Adding or updating the additional client ID

To add or update the Additional Client ID for an order:

1. Go to **Marketplace** > **Agreements**.
2. Select the required agreement.
3. On the **agreement details** page, select the **Details** tab, then select **Edit**. 

<div data-with-frame="true"><figure><img src="/files/dEtAGo3QshmUi2y8vwNz" alt=""><figcaption><p>Use the Edit option on the Details tab to update the additional client ID. </p></figcaption></figure></div>

4. In the **Edit ID** dialog, add or update the client ID, then select **Save**.&#x20;

The updated ID is displayed as a **Client ID** under **Additional IDs**. This same ID is also displayed on your invoice as the **PO number**.&#x20;

{% hint style="info" %}
If the value exceeds 20 characters, only the first 16 characters are shown on the invoice, followed by 3 dots (...). For more information, see [Understand your billing documents.](/modules-and-features/billing/understand-your-billing-documents.md)
{% endhint %}


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