Can't restrict Subscription creation with Azure Policy.

Question

We created the policy that should restrict the creation of new subscription, if it has any or all of the specific tags missing.

The policy is not restricting the creation of new subscription but, is marking the subscription "non-compliant" after it has been created, if any given tag is missing.

The Policy rule is like below:

"policyRule": {

  "if": {

    "allOf": [

      {

        "equals": "Microsoft.Resources/subscriptions",

        "field": "type"

      },

      {

        "anyOf": [

          {

            "exists": "false",

            "field": "tags['ProjectName']"

          },

          {

            "exists": "false",

            "field": "tags['Environment']"

          }

        ]

      }

    ]

  },

  "then": {

    "effect": "Deny"

  }

}  

Is is possible to restrict subscription creation using Azure Policy?