Can't invoke Soap method with Zeep and basic auth

Question

I am trying to access Web Service with Zeep and I get 401 in response. I checked official docs and https://stackoverflow.com/a/48861779/9187682 . I get an error when I try to call a method, like:

from requests import Session
from requests.auth import HTTPBasicAuth  # or HTTPDigestAuth, or OAuth1, etc.
from zeep import Client
from zeep.transports import Transport

session = Session()
session.auth = HTTPBasicAuth(user, password)
client = Client('http://my-endpoint.com/production.svc?wsdl',
    transport=Transport(session=session))

Items = client.get_type('ns1:ItemsType')
response = client.service.publishService('MyProps', Items ={ #ERROR HAPPENS HERE
    'ItemInformation': {
        '':''
    }
})

The response I get is:

zeep.exceptions.TransportError: Server returned response (401) with invalid XML: Invalid XML content received (Start tag expected, '<' not found, line 1, column 1).

Request in itself is OK (it works without auth if it's disabled on service).

Credentials are OK as well (in fact the whole thing works in Soap UI)

Am I missing something here?