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

# addon_purchased Event

> Track when a customer purchases an add-on feature or service.

Fires when a customer purchases an add-on feature or service. Use this event to measure add-on adoption and expansion revenue.

## JavaScript

```javascript theme={null}
window._upstack('track', 'addon_purchased', {
  accountId: 'acct_abc123',
  subscriptionId: 'sub_def456',
  addonId: 'addon_advanced_analytics',
  addonName: 'Advanced Analytics',
  price: 4900,
  currency: 'USD',
  billingInterval: 'month'
});
```

## Properties

| Property        | Type   | Required | Description                |
| --------------- | ------ | -------- | -------------------------- |
| accountId       | string | Yes      | Account identifier         |
| addonId         | string | Yes      | Add-on identifier          |
| subscriptionId  | string | No       | Subscription identifier    |
| addonName       | string | No       | Human-readable add-on name |
| price           | number | No       | Add-on price in cents      |
| currency        | string | No       | ISO 4217 currency code     |
| billingInterval | string | No       | `month` or `year`          |

## When to Fire

* When add-on is purchased from settings
* When add-on checkout completes
* When Stripe subscription item is added