If using a bucket to sync config validator policy, then a GCP project IAM policy binding tying the Kubernetes Service account for the config-validator (created by this chart) to the GCP IAM Forseti client service account. This binding is created via the Terraform module or can be created manually.
Would be good to update the doco here: https://hub.helm.sh/charts/forseti-security/forseti-security
Under prerequisites, to add: