Freemarker syntax for accessing item in array

I am trying to create a custom payload for my Webhook destination. The input event payload has an array of items and I always want to access fields in the first item of the array. I am able to successfully test the connection if I only access the first item of the array, but when I try to access properties within that item, I get a configuration error.

"${input.events[0].event_type}"

Leads to the error below

There was an issue with sending your test event.
Invalid payload or configuration.

But 

"${input.events[0]}"

does not lead to any errors. This suggests that accessing the item using the index works correctly, but I can’t find any documentation out there on how to access the properties within that item.

For reference, this is the input event. I redacted some private information. This is an integration between RevenueCat and Amplitude, I need to forward some of this info to another service (Singular) which Amplitude does not have an integration for.

{
  "api_key": <redacted>,
  "events": [
    {
      "event_properties": {
        "aliases": [
          <redacted>
        ],
        "app_id": <redacted>,
        "app_user_id": <redacted>,
        "cancel_reason": "UNSUBSCRIBE",
        "currency": "USD",
        "entitlement_id": null,
        "entitlement_ids": [
          "Default"
        ],
        "environment": "SANDBOX",
        "expiration_at": "2023-11-30T17:02:04Z",
        "original_app_user_id": <redacted>,
        "original_transaction_id": <redacted>,
        "period_type": "NORMAL",
        "presented_offering_id": null,
        "product_id": <redacted>,
        "purchased_at": "2023-11-30T16:02:04Z",
        "revenue": 0,
        "store": "APP_STORE",
        "subscriber_attributes": {
          "$fbAnonId": <redacted>,
          "$idfa": <redacted>,
          "$idfv": <redacted>,
          "$ip": <redacted>,
          "$onesignalId": <redacted>,
          "$onesignalUserId": <redacted>
        },
        "transaction_id": <redacted>
      },
      "event_type": "cancellation_event",
      "insert_id": <redacted>,
      "partner_id": "revenuecat",
      "platform": "iOS",
      "productId": <redacted>,
      "revenue": 0,
      "time": 1701360394149,
      "user_id": <redacted>,
      "user_properties": {
        "rc_subscription_status": "cancelled"
      }
    }
  ],
  "options": {
    "min_id_length": 5
  }
}