curl --request DELETE \
  --url https://api.x.com/2/users/{source_user_id}/following/{target_user_id} \
  --header 'Authorization: Bearer <token>'

{
  "data": {
    "following": true
  },
  "errors": [
    {
      "detail": "<string>",
      "status": 123,
      "title": "<string>",
      "type": "<string>"
    }
  ]
}