Azure runbook to start/stop a vm says "Completed" but nothing happens - powershell

Question

I'm quite new to Azure but I'm banging my head against something that seems simple. I've read a ton of resources that suggest this should be easy but I simply cannot get a runbook in the new portal (ARM) to start a specific VM. It runs and states "Completed" but nothing happens.
Here is the script:
Updated following Jack Zeng's comment which unfortunately changed little.
workflow StartDEVTC1
{
$VerbosePreference = "Continue"
$ErrorActionPreference = "Stop"
$WarnPreference = "Continue"
Write-Output "Getting credential..."
$cred = Get-AutomationPSCredential -Name 'AutomationPowershellCred1'
Write-Output "Adding account..."
Add-AzureRmAccount -Credential $cred
Write-Output "Getting VM..."
$VM = Get-AzureRmVM -ResourceGroupName "myResourceGroup" -Name "DEVTC1" -Status
$vmName = $VM.Name
$vmRG = $VM.ResourceGroupName
Write-Output "Checking state of $vmName from $vmRG..."
$VMDetail = $VM | Select-Object -ExpandProperty StatusesText | convertfrom-json
$vmPowerstate = $VMDetail[1].Code
if($vmPowerstate -like "PowerState/deallocated")
{
Write-Output "$vmName powerstate is $vmPowerstate, starting VM..."
$res = $VM | Start-AzureRmVM
if (($res.StatusCode) -ne 'OK')
{
Write-Error "Could not start VM."
}
}
else
{
Write-Output "$vmName powerstate is $vmPowerstate, not starting VM."
}
Write-Output "END."
}
As you can see I've tried adding some logging but I can't see these in the Testing Pane. Running the key steps in a Powershell on my PC works just fine so what's going on here?
The credential has been newly defined using the details of my azure account (I am an Owner on the account).
It should go without saying but I've tried some much simpler approaches to call Start-AzureRmVm and nothing works.
Thanks and appreciation in advance!

Answer 1

Ok I got it and the answer was frustratingly simple.
You cannot use a workflow block unless your runbook was created as a "PowerShell Workflow" runbook. In my case it was simply a "PowerShell" runbook which I guess was just ignoring the workflow block of code.
Recreating the runbook as a "PowerShell Workflow" runbook allowed the logging to be output so I could see what was happening and the VM got started as expected (although it took a really long time).