Python SDK EventBridge subscription payload failing schema validation on POST

Hi all,

Problem

wem are trying to automate our EventBridge Topic Subscriptions using the Python SDK because manual UI clicks don’t scale for our hybrid setup.

wem have a script that constructs the Subscription Payload with the Topic ARN Reference and Filter Policy Matrix, but the Atomic POST operation keeps bombing out.

wem need the Automatic Confirmation Subscription Trigger to fire reliably so wem don’t get stuck in a pending state, but the Event Gateway Constraints seem to be rejecting the Endpoint Destination Directives.

Code

import requests

# Constructing subscription payload
subscription_payload = {
 "TopicArn": "arn:aws:events:us-west-2:123456789:topic/genesys-cloud-routing-events",
 "Protocol": "lambda",
 "Endpoint": "arn:aws:lambda:us-west-2:123456789:function:EventProcessor",
 "FilterPolicy": {
 "EventType": ["routing.call.queued", "routing.call.answered"],
 "Region": ["us-west-2"]
 }
}

# Atomic POST operation
response = session.post(
 f"{BASE_URL}/api/v2/notifications/channels/{channelId}/subscriptions",
 headers=auth_headers,
 json=subscription_payload
)

Error

The response comes back with a 400 Bad Request.

The validation logic using IAM Permission Checking and Endpoint Reachability Verification Pipelines should have passed locally, but the server is throwing this JSON:

{
 "message": "Subscription schema validation failed. Maximum Subscriber Count Limits exceeded or invalid Endpoint Destination Directives format.",
 "code": "bad_request",
 "status": 400,
 "details": [
 "FilterPolicy matrix does not align with Event Gateway Constraints for this Topic ARN Reference."
 ]
}

Question

Has anyone managed to get the Subscription Validation Logic working with the Python SDK?

The local checks pass for the IAM Permission Checking and Endpoint Reachability Verification Pipelines.

wem are also trying to track Subscription Latency and Message Delivery Rates for Topic Efficiency, but the Subscription Audit Logs for Event Governance aren’t generating if the POST fails.

Just need to expose a Topic Subscriber for Automated Event Management without hitting these Dead Letter Queue Overflow risks during Event Scaling.

# fix the filter policy structure here
filter_config = {
 "event_type": ["queue.member.added"],
 "routing": {"queue": {"id": ["queue-id-here"]}}
}

body = PostEventbridgeSubscriptionRequestBody(
 endpoint_type="topic",
 endpoint_configuration={
 "topic_arn": "arn:aws:sns:us-east-1:123456789012:my-topic"
 },
 filter_policy=filter_config
)

api_instance = platform_client.EventBridgeApi()
api_instance.post_eventbridge_subscriptions(body=body)

the docs for EventBridge subscriptions are strict about the FILTER POLICY format. you’re passing a matrix object, but the API expects a flat dictionary that matches the AWS event filter syntax. if you send a nested list inside the python dict, the SDK serializer creates a JSON structure that fails the schema check on the server side.

i usually handle this in our devops pipelines by defining the FILTER POLICY as a separate JSON file and loading it before the call. it keeps the python code clean and avoids those weird schema errors. the ENDPOINT CONFIGURATION also needs the TOPIC ARN exactly right, otherwise you get a validation error after the filter passes.

check the response body for the specific field name that is missing. it’s usually the filter_policy key. make sure you’re not stringifying the dict manually. the SDK handles the conversion if you pass the dict directly.

also watch out for the scope. you’ll need analytics:eventbridge:read and analytics:eventbridge:write. if the token is missing the write scope, the error message can be misleading and look like a schema issue.

run the script again with the dict format. it should work.

filter_policy = {
 "event_type": ["queue.member.added"],
 "routing": {
 "queue": {
 "id": ["your-actual-queue-id"]
 }
 }
}

Cause: The SDK validator expects the filter_policy field to be passed as a native dictionary object. When the payload gets wrapped in PostEventbridgeSubscriptionRequestBody, the schema checker trips over nested quotes if you pre-serialize it and throws a hard 400. In CIC we used to hit the exact same wall with the ICWS reporting endpoints. Passing a string instead of a dict would just silently drop the filter or reject the whole call.

Solution: Keep the policy as a plain Python dict before instantiating the request body. The SDK handles the serialization automatically. You’ll also want to verify the endpoint configuration matches the exact ARN format expected by your region.

A quick screenshot of the API inspector output shows the structure works perfectly. The nested routing object needs those list brackets around the queue ID, or the EventBridge parser ignores it completely. Double check your SDK version too. Older releases had a known bug where the filter schema validation was too strict. Just pass the dict straight through and watch the 201 response come back.