Replace User msRTCSIP-GroupingID attribute with the OU ObjectGUID

Hello!

I am trying to create a script that will replace the users msRTCSIP-GroupingID attribute with the OU ObjectGUID

Can anyone help with this

Get-ADUser -Filter * -SearchBase "OU=Test,OU=Tenants,DC=Mayernetworks,DC=COM"
$OUobjectGUID = get-ADOrganizationalUnit -filter * -searchbase "ou=test,ou=tenants,dc=mayernetworks,dc=com" | ft ObjectGUID
Set-ADUser $Accounts -Add @{"msRTCSIP-GroupingID"=$OUobjectGUID}

i'm getting the argument is null error

bradley Wyatt