Iterate through a map of lists

I am trying to create custom security hub insights in AWS, there is a limitation on the number of items that can be passed in so I have split them up into 5 locals.

  guardrails = {
    guardrail_1 = [

    guardrail_2 = [
    guardrail_3 = [

    guardrail_4 = [

    guardrail_5 = [
      "waf-regional-rulegroup-not empty",

I am using for_each to loop through and create each insight name using the key from the local and I am trying to pass in the titles using the values but keep getting

Inappropriate value for attribute "value": string required.

This is the resource code

resource "aws_securityhub_insight" "security_guardrails_posture_cmp1" {
  for_each = local.guardrails

  name               = each.key
  group_by_attribute = "SeverityLabel"

  filters {

    dynamic "product_fields" {
      for_each = local.insights_account_ids
      content {
        comparison = "EQUALS"
        key        = "aws/securityhub/AwsAffectedAccountId"
        value      = product_fields.value

    workflow_status {
      comparison = "EQUALS"
      value      = "NEW"

    workflow_status {
      comparison = "EQUALS"
      value      = "NOTIFIED"

    record_state {
      comparison = "EQUALS"
      value      = "ACTIVE"

    title {
        comparison = "PREFIX"
        value      = each.value

How do iterate through the map of lists to pass in the strings?