Posting a story via graph.instagram.com works fine - but as soon as I add the parameter "user_tags" I get an error:

{ "error": { "message": "An unknown error has occurred.", "type": "OAuthException", "code": 1, "fbtrace_id": "AdG69JJokToh-pumknfZ..." } }

This is what my request looks like: https://graph.instagram.com/v21.0//media?access_token=xxx&media_type=STORIES&image_url=xxx&user_tags=[{username:'ersom'}]

Any ideas?