HttpRoute with sticky session

Traefik Traefik v3 (latest)
1

HI. I am trying to enable sticky sessions for a single application. I tried to follow the example at Kubernetes - Traefik for my own application, but I got an error:

dev01-traefik-95c7676d8-lzjx5 dev01-traefik 2025-08-22T12:32:06Z ERR Unable to load HTTPRoute backend: Cannot load HTTPBackendRef traefik.io/TraefikService/backend/elements-whats-next: unsupported HTTPBackendRef traefik.io/TraefikService/elements-whats-next http_route=elements-whats-next namespace=backend providerName=kubernetesgateway

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: elements-whats-next
  namespace: backend
spec:
  parentRefs:
    - group: gateway.networking.k8s.io
      kind: Gateway
      name: ingress-gateway
      namespace: traefik
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /elements-next-the-sequel/
      filters:
        - type: URLRewrite
          urlRewrite:
            path:
              type: ReplacePrefixMatch
              replacePrefixMatch: /elements-next-the-sequel/
      backendRefs:
        - group: traefik.io
          kind: TraefikService
          name: elements-whats-next
          weight: 1
---
apiVersion: traefik.io/v1alpha1
kind: TraefikService
metadata:
  name: elements-whats-next
  namespace: backend
spec:
  weighted:
    services:
      - name: elements-whats-next
        port: 80
        weight: 1
    sticky:
      cookie:
        name: sticky_cookie
        secure: true
        httpOnly: true
---
apiVersion: v1
kind: Service
metadata:
  name: elements-whats-next
  namespace: backend
  labels:
    app.kubernetes.io/name: elements-whats-next
spec:
  selector:
    app.kubernetes.io/name: elements-whats-next
  sessionAffinity: ClientIP
  type: ClusterIP
  ports:
    - name: http
      targetPort: http
      port: 80

I tried to check a few minor things:

kubectl get crd traefikservices.traefik.io
NAME                         CREATED AT
traefikservices.traefik.io   2025-05-30T17:58:08Z

kubectl get pods -n traefik -o jsonpath='{.items[0].spec.containers[0].image}'
docker.io/traefik:v3.4.3

kubectl get crd httproutes.gateway.networking.k8s.io -o yaml | grep version

gateway.networking.k8s.io/bundle-version: v1.2.1

Any help would be greatly appreciated. Feel free to ask me to provide any more information.