[Python] How can I send an alexa notification via proactive events ask_sdk_core python?

I'm trying to send a notification from my skill to Alexa using proactive events through the ask_sdk_model python interface.

At the moment I'm trying to test with the Alexa developer console. I've retrieved my client id/secret from the Alexa developer console, and managed to determine the user_id of the developer console.

I have the following, but it's giving me an ambiguous "Bad Reqeust" error:

from ask_sdk_core.api_client import DefaultApiClient
from ask_sdk_core.serialize import DefaultSerializer
from ask_sdk_model.services import ApiConfiguration, AuthenticationConfiguration
from ask_sdk_model.services.proactive_events import CreateProactiveEventRequest, RelevantAudience, RelevantAudienceType, SkillStage

ALEXA_CLIENT_ID = "XXX"
ALEXA_CLIENT_SECRET = "YYY"


def notify_alexa_device(user_id: int):
api_configuration = ApiConfiguration(serializer=DefaultSerializer(), api_client=DefaultApiClient())
authentication_configuration = AuthenticationConfiguration(
client_id=ALEXA_CLIENT_ID,
client_secret=ALEXA_CLIENT_SECRET,
)
client = ProactiveEventsServiceClient(
api_configuration,
authentication_configuration
)
notification_event = Event(
name="AMAZON.Occasion.Updated",
payload={
"state": {"confirmationStatus": "CONFIRMED"},
"occasion": {
"occasionType": "APPOINTMENT",
"subject": "localizedattribute:subject",
"provider": {"name": "localizedattributeroviderName"},
"bookingTime": "2018-11-20T19:16:31Z",
"broker": {"name": "localizedattribute:brokerName"},
},
}
)
localized_attributes = [
{"locale": "en-US", "providerName": "Provider Name", "subject": "Subject", "brokerName": "Broker Name"},
{"locale": "ja-JP", "providerName": "プロバイダー名", "subject": "件名", "brokerName": "ブローカー名"},
]
event_request = CreateProactiveEventRequest(
event=notification_event,
localized_attributes=localized_attributes,
relevant_audience=RelevantAudience(object_type=RelevantAudienceType.Unicast, payload=[str(user_id)]),
)
client.create_proactive_event(
create_proactive_event_request=event_request,
stage=SkillStage.DEVELOPMENT,
)



Any idea what is causing the "Bad Request", and how I can initiate a proactive event with ask_sdk_model?

Exception:

File "visitors/functions.py", line 62, in notify_alexa_device
client.create_proactive_event(
File "7qDsB67C/lib/python3.12/site-packages/ask_sdk_model/services/proactive_events/proactive_events_service_client.py", line 118, in create_proactive_event
access_token = self._lwa_service_client.get_access_token_for_scope(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "7qDsB67C/lib/python3.12/site-packages/ask_sdk_model/services/lwa/lwa_client.py", line 111, in get_access_token_for_scope
return self._get_access_token(scope)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "7qDsB67C/lib/python3.12/site-packages/ask_sdk_model/services/lwa/lwa_client.py", line 155, in _get_access_token
lwa_response = self._generate_access_token(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "7qDsB67C/lib/python3.12/site-packages/ask_sdk_model/services/lwa/lwa_client.py", line 234, in _generate_access_token
api_response = self.invoke(method="POST", endpoint=endpoint,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/lib/python3.12/site-packages/ask_sdk_model/services/base_service_client.py", line 151, in invoke
raise ServiceException(message=exception_metadata.message,
ask_sdk_model.services.service_exception.ServiceException: Bad Reques

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