Importing JSON always creates a new group

Hello, I’m importing a JSON file with redirections and it always creates a new group despite I have targeted a group_id (6) in the JSON…

The group exists (I can see it on the URL when seeing the redirections inside):

https://domain.com/wp-admin/tools.php?page=redirection.php&filterby%5Bgroup%5D=6

Any ideas? I’m doing something wrong?

The JSON I’m using is:

{
  "redirects": [
    {
      "url": "/category/postname/",
      "match_data": {
        "source": {
          "flag_query": "exact",
          "flag_case": false,
          "flag_trailing": false,
          "flag_regex": false
        }
      },
      "action_code": 410,
      "action_type": "error",
      "action_data": null,
      "match_type": "url",
      "group_id": 6,
      "enabled": true
    }
  ]
}

Thank you.