unable to get secret cert-manager; unable to get secret /cert-manager; resource name may not be empty

[matthias-hampel]

I get the error message unable to get secret cert-manager; unable to get secret /cert-manager; resource name may not be empty when trying to retrieve a certificate.

This is the error message from the cert-manager pod:

I0226 16:11:44.490477       1 dns.go:90] "presenting DNS01 challenge for domain" logger="cert-manager.controller.Present" resource_name="chart-example-tls-1-3937858742-2111318442" resource_namespace="hello" resource_kind="Challenge" resource_version="v1" dnsName="hello.mydomain.com" type="DNS-01" resource_name="chart-example-tls-1-3937858742-2111318442" resource_namespace="hello" resource_kind="Challenge" resource_version="v1" domain="hello.mydomain.com"
E0226 16:11:44.500764       1 controller.go:157] "re-queuing item due to error processing" err="unable to get secret `cert-manager`; unable to get secret `/cert-manager`; resource name may not be empty" logger="cert-manager.controller"

I created a secret (named hetzner-secret) in the cert-manager namespace which contains my DNS apiKey:

apiVersion: v1
kind: Secret
metadata:
  name: hetzner-secret
  namespace: cert-manager
data:
  api-key: base64encodedapikey

This is the Cluster Issuer config:

apiVersion: cert-manager.io/v1
kind: ClusterIssuer
metadata:
  name: letsencrypt-prod
spec:
  acme:
    server: https://acme-v02.api.letsencrypt.org/directory
    email: email@example.com
    privateKeySecretRef:
      name: letsencrypt-prod
    solvers:
      - dns01:
          webhook:
            groupName: acme.mydomain.com
            solverName: hetzner
            config:
              zoneName: mydomain.com
              apiUrl: https://dns.hetzner.com/api/v1

I do not really understand the error and hope, that you can help me to solve this problem.