`BadInputError: "No auth function for given request"` ...but I did.... So, what is happening?

It was working when I used the straight access token, but having to approve a new token every time the script was run was infeasible and irritating. So, I have migrated over to using a refresh_token, which has been successfully acquired and saved. Now I am attempting to test uploading file contents to a designated file in the box of drop-ness.

Traceback (most recent call last):
  File "/home/vassilios/Sandbox/orgzly-y-py/main.py", line 480, in <module>
    main()
  File "/home/vassilios/Sandbox/orgzly-y-py/main.py", line 471, in main
    dropbox_put(config['app_key'], config['dropbox_folder'],
  File "/home/vassilios/Sandbox/orgzly-y-py/main.py", line 389, in dropbox_put
    dropbox_upload(app_key, fullname, folder, name)
  File "/home/vassilios/Sandbox/orgzly-y-py/main.py", line 298, in dropbox_upload
    res = dbx.files_upload(
  File "/usr/local/lib/python3.9/site-packages/dropbox/base.py", line 3207, in files_upload
    r = self.request(
  File "/usr/local/lib/python3.9/site-packages/dropbox/dropbox_client.py", line 301, in request
    self.check_and_refresh_access_token()
  File "/usr/local/lib/python3.9/site-packages/dropbox/dropbox_client.py", line 369, in check_and_refresh_access_token
    self.refresh_access_token(scope=self._scope)
  File "/usr/local/lib/python3.9/site-packages/dropbox/dropbox_client.py", line 403, in refresh_access_token
    self.raise_dropbox_error_for_resp(res)
  File "/usr/local/lib/python3.9/site-packages/dropbox/dropbox_client.py", line 627, in raise_dropbox_error_for_resp
    raise BadInputError(request_id, res.text)
dropbox.exceptions.BadInputError: BadInputError('ba53047e1ac14efd97fac1e6ceea178f', '{"error": "invalid_request", "error_description": "No auth function available for given request"}')

The block of code generating the error should look very familiar to everyone, it is a stripped down and modified revision of the upload function from `updown.py` in the Dropbox repo. The biggest change in the function is removal of the unneeded call to `stopwatch`, and the addition of a request for new access token, which I "borrowed" from this forum. It is straight forward, which is why I am surprised to have received the error.

So here it is:

def dropbox_upload(app_key, fullname, folder, name, overwrite=False):
    """Upload a file.
    Return the request response, or None in case of error.
    """
    config = ConfigObj(DBX_CONFIG_FILE)
    REFRESH_TOKEN = config['dropbox_token']
    with dropbox.Dropbox(
            oauth2_refresh_token=REFRESH_TOKEN, app_key=app_key) as dbx:
        path = '/%s/%s' % (folder, name)
        while '//' in path:
            path = path.replace('//', '/')
        mode = (dropbox.files.WriteMode.overwrite
                if overwrite
                else dropbox.files.WriteMode.add)
        mtime = os.path.getmtime(fullname)
        client_modified = datetime.datetime(*time.gmtime(mtime)[:6])
        with open(fullname, 'rb') as f:
            data = f.read()
        try:
            res = dbx.files_upload(
                data, path, mode, client_modified=client_modified, mute=True)
        except exceptions.ApiError as err:
            print('*** API error', err)
            return None
        print('uploaded as', res.name.encode('utf8'))
        return res

I have searched through the OAuth guide and the Python SDK for references to this error, and did not find anything. So, why is this not working?

(corrected formatting 10-17 3:00pm)