MPower PHP Library Checkout Invoice Confirmation

confirm_invoice.php

<?php
// MPower will automatically set the confirm token to QUERY_STRING 
// param $_GET['token'] if not explicitly specified
$token = $_GET["token"];

$invoice = new MPower_Checkout_Invoice();
if ($invoice->confirm($token)) {

  // Retrieving Invoice Status
  // Status can be either completed, pending, canceled, fail
  print $invoice->getStatus();

  // You can retrieve the Name, Email & Phone Number 
  // of the customer using the callbacks below 
  print $invoice->getCustomerInfo('name');
  print $invoice->getCustomerInfo('email');
  print $invoice->getCustomerInfo('phone');
  
  // Return the URL to the Invoice Receipt PDF file for download
  print $invoice->getReceiptUrl();

  // Retrieving any custom data you have added to the invoice
  // Please remember to use the right keys you used to set them earlier
  print $invoice->getCustomData("Firstname");
  print $invoice->getCustomData("CartId");
  print $invoice->getCustomData("Plan");

  // You can also callback the total amount set earlier
  print $invoice->getTotalAmount();

}else{
  print $invoice->getStatus();
  print $invoice->response_text;
  print $invoice->response_code;
}

How do you get the transaction id. ? I know for direct payment it will be print $direct_pay->transaction_id;