You can use Retrieve a video endpoint to pull for the video status.

A video that has finished rendering may still be awaiting content moderation review. Until that review is final, the video is returned with in_progress status rather than complete, and its download, thumbnail and captions are not included. Keep polling until the status is complete.

Videos rejected by content moderation return a 404 response unless includeRejected is true, in which case they are returned with rejected status and without download, thumbnail or captions.