SendAs Permission in a Workflow with Add-ADPermission

Hello

I have a strange problem, with a Workflow.

The Idea behinde the Workflow is

• We have SharedMailboxes
• For Each SharedMailboxe we built a FullAccess and SendAs Group
• If user is added to the group the workflow starts and we are adding the SendAs Permission for the User via Powershell Script

The problem is that the Add-Permission command is executed according to the debug log, but the SendAs command is not set on the mailbox in the end. If I run the code outside of AR, with the Admin user for AR, by hardcoding a test object, setting the SendAs permission on the mailbox works fine.

Is there any reason why an Exchange Powershell command would not run within a workflow?

function SendAsAdd ($Request)
{
	#Var
	$ExchangeURL = "https://mail/PowerShell"
	$domainDN = "DC=XX,DC=CCC,DC=EEE"
	$Group = $workflow.SavedObjectProperties("Group").get("samAccountName")
	$Mail = $Group.Replace("_SENDAS", "")

	# Exchange Connection
	$SkipCertificate = New-PSSessionOption -SkipCACheck -SkipCNCheck -SkipRevocationCheck
	$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri $ExchangeURL -Authentication Basic -SessionOption $SkipCertificate -credential $DomainOverrideCredentials.get($domainDN)
	Import-PSSession -Session $Session -AllowClobber
	
	# Get Member of SendAs Group
	$SendASGroup = @()
	Get-ADGroupMember $Group | foreach {
		$SendASGroup += $_.SamAccountName
	}
	
	# Get Users that have send as permission on Mailbox
	$SendAS = @()
	Get-Mailbox -Identity $Mail | Get-ADPermission | ? { ($_.ExtendedRights -like "*send*") -and ($_.User -like "*ADDOMAIN*") } | foreach {
		$user = $_.User.split("\")[1]
		$SendAS += $user
	}
	
	# Compare Members of Group and User that have permission and if not entitled
	foreach ($MBXMember in $SendASGroup)
	{
		if ($SendAS -match $MBXMember)
		{		}
		else
		{
			$UserToAdd = Get-ADUser -Identity $MBXMember -Properties distinguishedName
			$MailboxUser = Get-ADUser -Identity $Mail -Properties distinguishedName
			Add-ADPermission -Identity $MailboxUser -User $UserToadd -AccessRights ExtendedRight -ExtendedRights "Send As"
		}
	}
	Remove-PSSession -Session $Session
}