gcp-audit mode attach service account

[sunnythakkar2005]

Hi,
I am trying to use a common service account to deploy policy in gcp-audit mode. However, when I try to deploy it , I get following error.

Exception running policy:gcp-monitor-public-bucket-notify-audit account:project_name region:global error:<HttpError 403 when requesting https://cloudfunctions.googleapis.com/v1/projects/project_name/locations/us-central1/functions/function?updateMask=serviceAccountEmail%2CsourceUploadUrl&alt=json returned "Missing necessary permission iam.serviceAccounts.actAs for cloud-functions-mixer on the service account service_account@<project>.iam.gserviceaccount.com. Grant the role 'roles/iam.serviceAccountUser' to cloud-functions-mixer on the service account service_account@nproject.iam.gserviceaccount.com.

any help would be appreciated