As renders may take a while to complete, it may be necessary to poll the GET /v1/renders endpoint several times to detect when a render is complete, which is clearly not very efficient. Rather than polling, consider setting up a webhook so Creatomate can notify you when a render is finished.
Ensure that your webhook endpoint is publicly accessible. Then, provide the webhook_url parameter with your POST request. The metadata parameter allows you to pass through data to your webhook for further processing. As soon as the render succeeds or fails, Creatomate will call your webhook endpoint with data of the type Render.
Your webhook should return a response instantly, otherwise its HTTP response code will not appear in your Creatomate dashboard under "API Log".