Traffic callout extension not working on Application Load Balancer

Google Cloud Compute Infrastructure
1

Trying to set up a traffic callout extension to an Application Load Balancer with VM instance group backends, following this wiki: https://cloud.google.com/service-extensions/docs/configure-callout

After adding the traffic-ext policy, the load balancer always returns

HTTP/1.1 500 Internal Server Error
date: Fri, 20 Oct 2023 13:19:57 GMT
via: 1.1 google
content-length: 0

Removing this extension makes the load balancer functional again

My extension yaml:

name: traffic-ext
loadBalancingScheme: EXTERNAL_MANAGED
forwardingRules:
- https://www.googleapis.com/compute/v1/projects/<project>/regions/us-west1/forwardingRules/l7-xlb-forwarding-rule
extensionChains:
- name: "chain1"
  matchCondition:
    celExpression: 'request.method=="GET"'
  extensions:
  - name: 'ext11'
    authority: <random url>
    service: https://www.googleapis.com/compute/v1/projects/<project>/regions/us-west1/backendServices/l7-ilb-callout-service
    failOpen: false
    timeout: 1s
    supportedEvents:
    - REQUEST_HEADERS
    - REQUEST_BODY
    - RESPONSE_HEADERS
    - RESPONSE_BODY
2

On setting failOpen to true, the lb doesnt return 500 anymore, but still my extension application is not at all invoked

3

The issue was that the grpc server was not listening on a tls port. It is working fine after the connection was made secure. Client auth is not required