How to enforce a policy on Azure Batch Pools Resource Tags

Hi!
I've been trying to define a policy that denies creation of a Pool in my Azure Batch account, unless it comes with specific Resource Tags during its creation.
I tried with the following terraform code snippet, which generally works well for other resources (such as storage account, resource groups etc.):

resource "azurerm_policy_definition" "tags_enforcement_policy" {
  name         = "Enforce-Required-Tags-On-Azure-Batch-Pools"
  policy_type  = "Custom"
  mode         = "All"
  display_name = "Enforce Required Tags on Azure Batch Pools"
  policy_rule = jsonencode({
    if = {
      allOf = [
        {
          field: "type",
          equals: "Microsoft.Batch/batchAccounts/pools"
        },
        {
          anyOf = [
            {
              field = "tags['required_tag']",
              exists = "false"
            }
          ]
        }
      ]
    },
    then = {
      effect = "deny"
    }
  })
}


resource "azurerm_resource_policy_assignment" "azure_batch_tag_enforcement_assignment" {
  name                 = "azure-batch-tag-enforcement-assignment"
  resource_id          = azurerm_batch_account.mybatchaccount.id
  policy_definition_id = azurerm_policy_definition.tags_enforcement_policy.id
}

While the policy itself is applied correctly, this prevents creating of all Batch Pools, even if the expected required_tag is added.
Upon further investigation I realised that Batch Pools have Resource Tags, but these are not to be confused with the actual resource-level tag that understood by Azure Policy or Azure

I tried the following test, along many others:

policy_rule = jsonencode({
  if = {
    allOf = [
      {
        field: "type",
        equals: "Microsoft.Batch/batchAccounts/pools"
      },
      {
        anyOf = [
          {
            field = "Microsoft.Batch/batchAccounts/pools/resourceTags.required_tag",
            exists = "false"
          }
        ]
      }
    ]
  },
  then = {
    effect = "deny"
  }
})

But this is not recognised as a correct policy definition.

I am wondering: is there a way to check existence of Batch Pool resource tag with Azure Policy?
If no, are automated scripts the only solution?

Thank you!