represent helm chart values.yaml in helmfile.yaml

I am trying to represent the following in the helmfile.yaml but I am getting an error. Can anyone help me to set it up?

values.yaml

extraVolumes:
 - name: google-cloud-key
   secret:
     secretName: gcloud-auth

I tried the following in helmfile.yaml

repositories:
  - name: loki 
    url: https://grafana.github.io/loki/charts

releases:
  - name: loki
    namespace: monitoring
    chart: loki/loki
    set: 
    - name: extraVolumes.name
      value: google-cloud-key
    - name: extraVolumes.secret.secretName
      value: gcloud-auth

The error I am getting is

coalesce.go:160: warning: skipped value for extraVolumes: Not a table.

I also tried with the following in helmfile.yaml

    - name: extraVolumes.name[]
      value: google-cloud-key

This gave me the following error

Error: failed parsing --set data: key map "extraVolumes" has no value

Any idea?