Is it possible to reference the referrer URL when configuring a webhook, and if so, how?

I’m trying to use the advanced option to POST the referrer as part of the webhook body, not unlike this:

```

{

    “data”: {

        “referrer_url”: “{{ticket.what_goes_here}}”

    }

}

```

None of the placeholder options seem correct, but maybe it’s called something weird and I’m just missing it (I also can’t find anywhere I can see a sample of values, like you can in zappier for example).