How to monitor IP allocation in Azure subnet?

I need to find the current usage of IP addresses within subnets in Azure. I found free IPs in Virtual Networks->subnets but the number is the total available IP addresses within the subnet. How can I see how many of the available IPs within the subnet are actually in use (how many of them are free)? Is there a way to set the monitoring for free IP addresses (or used IP addresses) for Azure subnets? Thanks in advance.

Solution

You can call the listUsage API /subscriptions/****/resourceGroups/aoprod9574-stamp-canadacentral-rg/providers/Microsoft.Network/virtualNetworks/vnet-name/usages?api-version=2021-02-01 to get the current allocations per Subnet in a VNet

{
  "value": [
    {
      "currentValue": 3,
      "id": "/subscriptions/****/resourceGroups/my-rg/providers/Microsoft.Network/virtualNetworks/aoprod9574-canadacen-vnet/subnets/cosmosdb-pe-snet",
      "limit": 27,
      "name": {
        "localizedValue": "Subnet size and usage",
        "value": "SubnetSpace"
      },
      "resourceGroup": "my-rg",
      "unit": "Count"
    },
    {
      "currentValue": 93,
      "id": "/subscriptions/****/resourceGroups/my-rg/providers/Microsoft.Network/virtualNetworks/aoprod9574-canadacen-vnet/subnets/kubernetes-snet",
      "limit": 1019,
      "name": {
        "localizedValue": "Subnet size and usage",
        "value": "SubnetSpace"
      },
      "resourceGroup": "my-rg",
      "unit": "Count"
    }
  ]
}