Can't correctly pass timestamp to ElasticSearch

[neolunar7]

When I deploy k8s event exporter with the setting below, I get the error below.

    logLevel: debug
    receivers:
      - name: "es"
        elasticsearch:
          hosts:
          - MYHOST
          index: kube-events
          layout:
            message: "{{ .Message }}"
            reason: "{{ .Reason }}"
            type: "{{ .Type }}"
            kind: "{{ .Kind }}"
            name: "{{ .InvolvedObject.Name }}"
            namespace: "{{ .InvolvedObject.Namespace }}"
            creationtime: "{{ .Metadata.CreationTimestamp }}"
    route:
      routes:
        - match:
            - receiver: "es"

│ 2021-06-08T14:40:05Z DBG bitnami/blacksmith-sandox/kubernetes-event-exporter-0.9.0/src/gitrhub.com/opsgenie/kubernetes-event-exporter/pkg/exporter/channel_registry.go:59 > Cannot send event error="template: template:1:19: executing \"template\" at <.Metadata.CreationTimetstamp>: can't evaluate field Metadata in type *kube.EnhancedEvent"

How can I correctly pass timestamp format into Elasticsearch ?