Meta /media_publish return 500 unknown error

I'm using the Instagram Graph API via https://graph.facebook.com/v21.0 to publish both images and videos on Instagram. Publishing images works without issues, but I'm encountering a problem when attempting to publish videos.

Here’s my process:

1. Create Media Container for Video

I create a media container using the following request:

POST https://graph.facebook.com/v21.0/<user-id>/media {    video_url: video.mp4 (744k, 18s long H264 MPEG-4 AAC)    caption: caption    media_type: REELS    share_to_feed: true    access_token: ... } 

2. Publish Media Using the Container ID Then, I attempt to publish the video with this request:

POST https://graph.facebook.com/v21.0/<user-id>/media {     creation_id: <id-container>     access_token: ... } 

However, this returns a 500 error:

{     "error": {         "message": "An unknown error has occurred.",         "type": "OAuthException",         "code": 1,         "fbtrace_id": <trace-id>     } } 

I can't find anything on the community forum and the bug report is not working either. Any idea what I could try?