Gitlab Kubernetes Agent GraphQL: Field 'createClusterAgent' doesn't exist on type 'Mutation'

I am following this official doc GitLab Kubernetes Agent | GitLab for setting up Gitlab Kubernetes Agent for my own Gitlab CE instance (docker image gitlab/gitlab-ce:13.11.3-ce.0 with gitlab_kas['enable'] = true in GITLAB_OMNIBUS_CONFIG).

Trying to run the documented GraphQL code with https://gitlab.my-own-domain.com/-/graphql-explorer :

  mutation createAgent {
    # agent-name should be the same as specified above in the config.yaml
    createClusterAgent(input: { projectPath: "path-to/your-configuration-project", name: "<agent-name>" }) {
      clusterAgent {
        id
        name
      }
      errors
    }
  }

Gitlab returns this error output:

{
  "errors": [
    {
      "message": "Field 'createClusterAgent' doesn't exist on type 'Mutation'",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "mutation createAgent",
        "createClusterAgent"
      ],
      "extensions": {
        "code": "undefinedField",
        "typeName": "Mutation",
        "fieldName": "createClusterAgent"
      }
    }
  ]
}

Can you please lead me how to fix it?

I faced the same problem.
Probably, I need Premium edition.