IG User Connected Threads User

• You need to have at least an Advertiser role on the Page that is linked to your Instagram account; Manager or Content Creator also work. Or you need to have the Instagram account connected to a business account where you have appropriate roles.
• If you want to use this Threads account ID for Threads ads creation, make sure your connected Instagram account has the correct ads creation identity setup, either business-claimed Instagram account or page-connected Instagram account.
• An Instagram account can have only one Instagram-connected Threads account. Verify whether a specific Instagram account has an Instagram-connected Threads account before attempting to create a new one. If one already exists, use that one.

curl -G \
  -d "access_token=<ACCESS_TOKEN>"\
  -d "fields=threads_user_id" \
"https://graph.facebook.com/v25.0/<IG_USER_ID>/connected_threads_user"

{
  "data": [
    {
      "threads_user_id": "<THREADS_USER_ID>",
    }
  ],
}