Python Django Interaction with Third Party Backend via Client Library - django

Question

I am programming a web frontend and backend with Python Django for a FinTS client (https://python-fints.readthedocs.io/en/latest/).
The FinTS client library provides an API to communicate with a third party backend.
The communication with the FinTS client has to be done in multiple steps:
first connect
then the backend asks for a TAN number
the TAN number has to be provided
then transactions can be fetched
Basically the sequence looks like this:
Sequence
I am struggling with the question how I could realize this in detail with Django.
I did some experiences with Django, Django Channels and Websockets, but without real success.
I tried so far:
A Django view provides a Django form
The web client creates a websocket connection to a WebSocketConsumer
The WebSocketConsumer provides its Django channel name to the web client
The web client posts the form with credentials including the channel name
When the form is posted, the view sends a message via a Django Channel to a BackgroundWorker inlcluding the web socket channel name
The BackgroundWorker instantiates the FinTS client object and initiates the connection.
The BackgroundWorker sends a message to the WebSocketConsumer asking for the TAN
The WebSocketConsumer sends a web socket message to the web client to ask for the TAN
The web client sends the TAN via web socket message
Here I have the following problems:
Sending the message from the Django View to the BackgroundWorker in step 5 results in a weired type error (https://github.com/redis/redis-py/issues/2593)
ile "/mnt/d/Documents/python/myapp/myapp/.venv/lib/python3.8/site-packages/redis/asyncio/client.py", line 547, in parse_response
retval = self.response_callbacks[command_name](response, **options)
TypeError: int() argument must be a string, a bytes-like object or a number, not 'NoneType'
2.
Even if this worked, the BackgroundWorker needs to instantiate the FinTS client object
class BackgroundWorker (AsyncConsumer):
async def start(self, event):
f = FinTS3PinTanClient(*client_args)
But where to store the reference f to the object for a specific client ? When the function terminates, the object is lost, but I still need later for sending the TAN number and requesting the transactions.
It seems that the FinTS library supports to serialize the current state, destruct the object and later reconstruct it with the serialized data.
But where to store the serialized data? In the database?
Alternatively the BackgroundWorker would somehow need to block and wait for another message from the WebSocket client. But this does not seem to be a good idea.
Is the approach with the BackgroundWorker the right idea?
Is a pure Websocket approach better? But I would like to use Django forms for the credentials form.
Maybe I am totally on the wrong track.
I am not so familiar with web frontends and backends - can somebody give me a hint how you would design the architecture could in a real production system?