Start-AzVM : Cannot bind parameter ‘DefaultProfile’ when running an Azure runbook

I am working on this official tutorial from MS Azure team to run a PowerShell Workflow runbook to start a VM. But when I start the following runbook (from step 6 of the tutorial), I get the error shown below. Question: What I may be missing, and how can we resolve the issue?

Remark: Start-AzVM is from Az.Compute module that I have already imported.

rinbook code:

workflow MyFirstRunbook-Workflow
# Ensures that you do not inherit an AzContext in your runbook
Disable-AzContextAutosave –Scope Process

$Conn = Get-AutomationConnection -Name AzureRunAsConnection
Connect-AzAccount -ServicePrincipal -Tenant $Conn.TenantID -ApplicationId $Conn.ApplicationID -CertificateThumbprint $Conn.CertificateThumbprint

$AzureContext = Get-AzSubscription -SubscriptionId $Conn.SubscriptionID

Start-AzVM -Name 'vm-cs-web01' -ResourceGroupName 'rg-cs-ansible1' -AzContext $AzureContext


Start-AzVM : Cannot bind parameter 'DefaultProfile'. Cannot convert the "a76c7e8f-210d-45e5-8f5e-525015b1c881" value of 
type "Deserialized.Microsoft.Azure.Commands.Profile.Models.PSAzureSubscription" to type 
At MyFirstRunbook-Workflow:11 char:11
    + CategoryInfo          : InvalidArgument: (:) (Start-AzVM), ParameterBindingException
    + FullyQualifiedErrorId : CannotConvertArgumentNoMessage,Microsoft.Azure.Commands.Compute.StartAzureVMCommand