I have been following this guide to create an nginx-ingress which works fine.

Next I want to create a ClusterIssuer object called letsencrypt-staging, and use the Let's Encrypt staging server but get this error.

kubectl create -f staging_issuer.yaml

error: unable to recognize "staging_issuer.yaml": no matches for kind "ClusterIssuer" in version "certmanager.k8s.io/v1alpha1"

I have searched for solutions but can't find anything that works for me or that I can understand. What I found is mostly bug reports.

Here is my yaml file I used to create the ClusterIssuer.

apiVersion: certmanager.k8s.io/v1alpha1
kind: ClusterIssuer
metadata:
 name: letsencrypt-staging
spec:
 acme:
   # The ACME server URL
   server: https://acme-staging-v02.api.letsencrypt.org/directory
   # Email address used for ACME registration
   email: your_email_address_here
   # Name of a secret used to store the ACME account private key
   privateKeySecretRef:
     name: letsencrypt-staging
   # Enable the HTTP-01 challenge provider
   http01: {}