I am trying to post a video through the Threads API in a single-thread post.

I upload the video to a public URL, using Vercel Blob, and I have verified that the video is there.

I use the POST /{threads-user-id}/threads endpoint to create a media container successfully.

When I use the POST /{threads-user-id}/threads_publish endpoint to publish the container, I get an error, stating: "The media with id {container-id} cannot be found."

The Threads API Troubleshooting page says: "If you are able to create a container for a video but the POST /{threads-user-id}/threads_publish endpoint does not return the published media ID, then you can get the container's publishing status by querying the GET /{threads-container-id} endpoint. ... We recommend querying a container's status once per minute, for no more than 5 minutes."

So I waited for 60 seconds and then queried the GET /{threads-container-id} endpoint, but it returns the following error:

{
  status: 'ERROR',
  error_message: 'UNKNOWN',
  id: '{threads-container-id}'
}

The same code successfully publishes a single-thread post with an image (using the image_url parameter instead of video_url, of course).

I have also verified that the video conforms to Threads' Video Specifications (screenshot attached).

Any suggestions are welcome.

Thanks, Michael