curl "https://app.tatango.com/api/v2/lists/ID/webhooks/WEBHOOK_ID" -d '{"webhook":{"url":"https://example.com/webhook"}}' -X PUT \
  -H "Accept: application/json" \
  -H "Content-Type: application/json" \
  -u emailaddress@mydomain.com:my_api_key \
  -H "Host: example.org" \
  -H "Cookie: "

{
  "status": "Webhook updated",
  "webhook": {
    "callback_url": "http://localhost.dev/null?api_key=foo_bar_baz",
    "created_at": "2016-09-07T14:11:13-07:00",
    "enabled": true,
    "id": 4,
    "list_id": 29,
    "message_sent": false,
    "subscribe": true,
    "unsubscribe": true,
    "updated_at": "2016-09-07T14:11:13-07:00"
  }
}