lab 10.1 step 9 error

I am following the steps exactly, and when executing

kubectl create -f ingress.rule.yaml

I am getting the following error:

error: error validating "ingress.rule.yaml": error validating data: [ValidationError(Ingress.spec.rules[0].http.paths[0].backend): unknown field "serviceName" in io.k8s.api.networking.v1.IngressBackend, ValidationError(Ingress.spec.rules[0].http.paths[0].backend): unknown field "servicePort" in io.k8s.api.networking.v1.IngressBackend]; if you choose to ignore these errors, turn validation off with --validate=false

any help appreciated

ingress.rule.yaml is

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: ingress-test
annotations:
kubernetes.io/ingress.class: traefik
spec:
rules:
- host: www.example.com
http:
paths:
- backend:
serviceName: secondapp
servicePort: 80
path: /