How to link the network group ID of a network manager to the policy

Question

I get a warning message when I run the code to populate the network groups using azure policy.

Warning: use-resource-id-functions: If property "networkGroupId" represents a resource ID, it must use a symbolic resource reference, be a parameter or start with one of these functions: extensionResourceId, guid, if, reference, resourceId, subscription, subscriptionResourceId, tenantResourceId.

I have tried using the resourceId function to link the network group to the policies but I also get this error message:

Validation Errors: 'String' /subscriptions/<subscriptionID>/providers/Microsoft.Network/networkManagers/<networkManagerName>/networkGroups/<networkGroupName>' does not match regex pattern. Path 'networkGroupId' 

How best can I add the networkGroupId without getting the warning message? Here is the policy code written in bicep.

 targetScope = 'subscription' 

 param tagName string
 param resourceGroupName string 
 param networkManagerName string 
 param networkGroupName string 

 var policyName = ''
 var policyDisplayName = '' 
 
 resource policyDefinition 'Microsoft.Authorization/policyDefinitions@2021-06-01' = {
   name: policyName
   properties: {
     displayName: policyDisplayName
     policyType: 'Custom'
     mode: 'Microsoft.Network.Data'
     metadata: {
       category: 'Virtual Network Manager'
     }
     parameters: {
       tagName: {
         type: 'String'
         metadata: {
           displayName: 'Tag name'
         }
       }
     }
     policyRule: {
       if: {
         allOf: [
           {
             field: 'type'
             equals: 'Microsoft.Network/virtualNetworks'
           }
           {
             allOf: [
               {
                 "field": "tagName",
                 "contains": "gen"
               }
             ]
           }
         ]
       }
       then: {
         effect: 'addToNetworkGroup'
         details: {
           networkGroupId: '${subscription().id}/resourceGroups/${resourceGroupName}/providers/Microsoft.Network/networkManagers/${networkManagerName}/networkGroups/${networkGroupName}'
         }
       }
     }
   }
 }