Consume webservice, problem with datetime

I have this code to consume a webservice

# -*- coding: utf-8 -*-
import zeep
import datetime
from zeep import Client
from zeep.transports import Transport
from zeep import xsd
from zeep.wsse.username import UsernameToken
from requests import Session
from requests.auth import HTTPBasicAuth
from datetime import datetime, timedelta, date
import pytz


url = 'https://facturaelectronica.dian.gov.co/habilitacion/B2BIntegrationEngine/FacturaElectronica/facturaElectronica.wsdl?'
client = Client(wsdl=url )
doc = 'Hello World'.encode()

#obtener fecha y hora actual / convertir en format datetime
formato='%Y-%m-%dT%H:%M:%S.523Z'
tz = pytz.timezone('America/Bogota')
created = datetime.now(tz)
print (created)
print (type(created))


header = zeep.xsd.Element(
        'Security',
        zeep.xsd.ComplexType([
            zeep.xsd.Element(
                'UsernameToken',
                zeep.xsd.ComplexType([
                    zeep.xsd.Element('Username',zeep.xsd.String()),
                    zeep.xsd.Element('Password',zeep.xsd.String()),
                    zeep.xsd.Element('Nonce',zeep.xsd.String()),
                    zeep.xsd.Element('Created',zeep.xsd.String()),

                ])
            ),
        ])
    )

factory = client.type_factory('ns0')
data = factory.EnvioFacturaElectronica()
data.NIT = "901193767"
data.InvoiceNumber = "9011937670"
data.IssueDate = created
data.Document = doc
print (data)
print (data.IssueDate)
print (type(data.IssueDate))

header_value = header(UsernameToken={'Username':'fd0653b3-6dd0-45cd-b2f6-bb108ac83a3a','Password':'6361b7b5322acb07ced00a35a85a4cc5183da3a42ede0b07f578067a18425a55', 'Nonce':'pHgdgwGne5Jw+yHy6SdcyQ==','Created':created})
node = client.service.EnvioFacturaElectronica(
                            _soapheaders=[header_value], *data
                            )

When I run the script I get the following error:

TypeError: combine() argument 1 must be datetime.date, not str

Will someone please execute the script and highlight what is the problem?