Error about permission with Powershell command Get-AzureStorageBlob in Azure Runbook

Question

I'm trying to create a runbook in Azure that accesses a blob storage and list the contents. But I keep getting the following error:

The remote server returned an error: (403) Forbidden. HTTP Status Code: 403 - HTTP Error Message: This request is not authorized to perform this operation using this permission.

I checked the following:
Azure Portal -> Storage Account -> Networking -> Check Allow Access From (All Networks / Selected Networks)
It is set to all networks.

I checked the SAS. It's correct.

On the storage account and the container I set the Access Control to Storage Blob Data Reader and Sotrage Blob Data Owner to Managed Identity\Automation Account

i created an Access Policy and set its rights to rdl, but I don't know how to call it from within my Powershell statement. I don't know whether it makes any difference.

Who can help me? I've about read all the articles on Internet but can't find the answer.

It's the statement Get-AzureStorageBlob that fails.

This is the code in the runbook:

$storage = "opslag" #name of storage account
$blobcontainer = "contener" #name of container
$sas = "****"

Write-Output $storage
Write-Output $container

$context = New-AzureStorageContext -StorageAccountName $storage -SasToken $sas
Write-Output $context

$blobs = Get-AzureStorageBlob -Container $blobcontainer -Context $context

Write-Output "Klaar!"