Don't understand how to upload a csv using the new api for it

[Neutrinzu]

Hi,
I'm pretty new to Superset and APIs in general.
I'm trying to upload a csv file with the new csv_upload feature with the API. (#27840)
With the following Python function I only get Error: 400 with the message "file":["Field may not be null."], "table_name":[Missing data for required field.".
Code Snippet:

def new_Upload(filepath_local, table_name, pk):
  csv_post = f"{SUPERSET_HOST}/api/v1/database/{pk}/csv_upload"
  upload_header = {
    "Authorization": f"Bearer {access_token}",
    "Content-Type": "multipart/form-data"
  }

    fields = {
        "table_name":table_name,
        "file":open(filepath_local, "rb")
    }

    response = requests.post(csv_post, files=fields, headers=upload_header)

    if response.status_code == 200:
        print(response.json()["message"])
    else:
        print(f"Error: {response.status_code} - {response.text}")

filepath = "C:/path/to/file.csv"
base_name = os.path.basename(filepath)
table_name, ext = os.path.splitext(base_name)
db_id = 1

new_Upload(filepath, table_name, db_id)

If i print out response.request.body it seems that the contents of the file and the keys "file" and "table_name" are in there.
I've tried to add "data" to the request post, which also containted the table name and file keys, but everything just responses to the error that the fields are empty.
Also uploading via form in the UI is working.
I'd appreciate some help.