Programmatically configure PIM for Azure subscription role resource

Question

According to the documentation here it is possible to call Azure API's to configure PIM for Azure resources, I am trying to set this up at the subscription level, i.e contributor for a subscription.

I have the script as follows.

Connect-AzAccount

# Variables

I get the error.

Invoke-RestMethod : {"error":{"code":"SubjectNotFound","message":"The subject is not found."}}
At line:1 char:13
+ $response = Invoke-RestMethod -Method Put -Uri $url -Headers $headers ...
+             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-RestMethod], WebExc
   eption
    + FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeRestMethodCommand