Python stripe can't delete connect account | 'str' object has no attribute 'refresh_from'

I am using stripe connect and a custom interface to create/manage stripe users.

I want now to delete a stripe connect account, the balance is 0 ofc., eventhough it should not matter with test keys. According to the docu for stripe connect it is super simple to delete an account:

With Connect, you may delete Custom accounts you manage.
Custom accounts created using test-mode keys can be deleted at any time. Custom accounts created using live-mode keys may only be deleted once all balances are zero.

That is my code:

user = User.query.filter_by(id=data_received["user_id"]).first()

stripe_acc_id = user.stripe_connect_acc_id

db_session.delete(user)

if stripe_acc_id != None:
    print ("User has stripe connect account", stripe_acc_id)
    try:
        stripe.Account.delete(stripe_acc_id)
    except Exception as e:
        return json.dumps({'status': 'failed', 'reason': str(e)})

db_session.commit()

But it does not work, I am getting this error:

{"status": "failed", "reason": "'str' object has no attribute 'refresh_from'"}