Case creation alert not being sent to specific Resource

Summary:

In case management I only want the Case Managers to be notified when a new case is created. I wrote a script to specifically send a notification to a specific Case manager by using their Party ID in app composer but it seems like they are not being notified at all. Please find my script below. I am also using the BeforeInsert trigger :

try {

println("Preparing data to send notification.");

def map = new HashMap();

// Notification message

def messageText = "A new unassigned case has been created: " + CaseNumber;

// Assigned Party ID

def recipientPartyId = AssigneeResourceId;

// List of allowed assignee Party IDs

def allowedAssigneeIds = [300000024550281];