docs: document subscription charge billing cycles

content/docs/admin-api/guides/subscription-management.mdx

@@ -123,6 +123,29 @@ The endpoint returns the full subscription object with updated renewal details o
 The subscription must be in an `active` status to trigger a renewal. For subscriptions in `past_due` status, use the [subscriptionsRetryCreate](/docs/admin-api/reference/subscriptions/subscriptionsRetryCreate) endpoint instead.
 </Callout>
 
+### Identifying Subscription Charges
+
+When a `transaction.created` webhook is associated with a subscription, `data.subscription` contains the subscription ID and billing cycle:
+
+```json title="Subscription Transaction"
+{
+    "event_type": "transaction.created",
+    "data": {
+        "id": 10416,
+        "subscription": {
+            "id": 12345,
+            "billing_cycle": 3
+        }
+    }
+}
+```
+
+- `billing_cycle: 0` identifies the initial subscription charge.
+- `billing_cycle: 1` identifies the first renewal.
+- Each subsequent renewal increments the value by one.
+
+The subscription object is empty when the transaction is not associated with a subscription.
+
 ### Updating Payment Details
 
 Updating the Payment Gateway of a subscription can done through the [subscriptionsPartialUpdate](/docs/admin-api/reference/subscriptions/subscriptionsPartialUpdate) endpoint.

content/docs/webhooks/index.mdx

@@ -72,6 +72,10 @@ Returning a `410` response code indicates the target resource is no longer avail
 | `ticket.created`          | Triggers a new support ticket is created. |  [View Example](/docs/webhooks/reference/support/ticket.created) |
 | `ticket.updated`          | Triggers when an existing support ticket is updated. | [View Example](/docs/webhooks/reference/support/ticket.updated) |
 
+<Callout type="info" title="Handling subscription charges">
+The `subscription` object on a `transaction.created` webhook links the charge to its subscription and identifies the billing cycle. See [Identifying Subscription Charges](/docs/admin-api/guides/subscription-management#identifying-subscription-charges).
+</Callout>
+
 ### Webhook Data Structure
 
 Webhook payloads follow the same structure as Admin API data serializers, which makes them predictable. In general, the data in a webhook payload matches the data you would get by retrieving the same resource through the API. You can set up test webhooks and view the webhook logs in the dashboard to help build and verify your receiver.