Extracting variables from calling the value- Getting Error message in condition

I am trying to do validation. checking the deployed values with the given values. I extract the vnet values from Azure resources using RestAPI method and convertto-json from Object because of vnet object is giving me empty object (@{value=System.Object[]}). The following is the Json code I am getting:

{
  "value": [
    {
      "properties": "@{virtualNetworkSubnetId=/subscriptions/<XXXX>/resourceGroups/<XXXX>/providers/Microsoft.Network/virtualNetworks/<XXXX>/subnets/<XXXX>; ignoreMissingVnetServiceEndpoint=True; state=Ready}",
      "id": "/subscriptions/<XXXX>/resourceGroups/<XXXX>/providers/Microsoft.DBforPostgreSQL/servers/<XXXX>/virtualNetworkRules/<XXXX>",
      "name": "<XXXX>",
      "type": "Microsoft.DBforPostgreSQL/servers/virtualNetworkRules"
    }
  ]
}

The following powershell command is to compare the value but getting an error saying $vnet.name and $vnet.id is $null

$vnet= ( $vnet | ConvertTo-Json)

   It "has this number of vNet Rules defined: $($config.vnetRules.count)" 
  {
    $vnet.count | Should -Be $config.vnetRules.count    
   }

   #$vnet.count is working and giving an success message

   foreach ($vnetRule in $config.vNetRules) {

    Write-Host $vnet            #-> getting Json 
    Write-Host $vnet.Name       #-> return as Empty($null)
        Write-Host $vnet.value.Name #-> return as Empty($null)
    Write-Host $vnet.id         #-> return as Empty($null)
        Write-Host $vnet.value.id   #-> return as Empty($null)

    it "has a vNet rule named: $($vnetRule.ruleName)" {
        $vnet.name | Should -Be $vnetRule.ruleName
    }

    it "has a vNet Rule Subnet ID of: $($vNetRule.subnetId)" {
        $vnet.value.id | Should -Be $vNetRule.subnetId
    }

}

Returns $null.

In my attempt to recreate your invoke-restmethod output, I used your JSON packet as input to create the $vnet variable.

I believe the problem is you are using Write-host to display the object instead of simply the object name. Write-host will attempt to convert the complex object to a string and hence you see the weird output as you can see below. see the difference when i simply out the object?

Now, $vnet has 4 properties id, name, properties, type and can be invoked as shown. In you case, you have converted the variable $vnet to json and then attempting to display its properties. But Json does not have any properties, except length. And hence, invoking those properties will give you null.