The first webhook invocation is immediately after the transcript is ready. We make an HTTP POST request to the customers callback_url. We expect a 200 response from the customer to acknowledge their receipt of our request. When we get the 200 response we will not make another request to the callback_url. If we do not get a 200 response we retry the webhook every 30 minutes for a total of 24 hours. After 24 hours, the transcript is still available using the GET /transcript endpoint, but we will not try the callback_url anymore.
There is one more status code we listen for. If a customer wants to unsubscribe from the webhook invocation they can respond to our webhook request with a 410 stats code.