PayPal\Api\CancelNotification::setSubject PHP Method

    public function setSubject($subject)
    {
        $this->subject = $subject;
        return $this;
    }

<?php

// # Cancel Invoice Sample
// This sample code demonstrate how you can cancel
// an invoice.
/** @var Invoice $invoice */
$invoice = (require 'SendInvoice.php');
use PayPal\Api\CancelNotification;
use PayPal\Api\Invoice;
try {
    // ### Cancel Notification Object
    // This would send a notification to both merchant as well
    // the payer about the cancellation. The information of
    // merchant and payer is retrieved from the invoice details
    $notify = new CancelNotification();
    $notify->setSubject("Past due")->setNote("Canceling invoice")->setSendToMerchant(true)->setSendToPayer(true);
    // ### Cancel Invoice
    // Cancel invoice object by calling the
    // static `cancel` method
    // on the Invoice class by passing a valid
    // notification object
    // (See bootstrap.php for more on `ApiContext`)
    $cancelStatus = $invoice->cancel($notify, $apiContext);
} catch (Exception $ex) {
    // NOTE: PLEASE DO NOT USE RESULTPRINTER CLASS IN YOUR ORIGINAL CODE. FOR SAMPLE ONLY
    ResultPrinter::printError("Cancel Invoice", "Invoice", null, $notify, $ex);
    exit(1);
}
// NOTE: PLEASE DO NOT USE RESULTPRINTER CLASS IN YOUR ORIGINAL CODE. FOR SAMPLE ONLY
ResultPrinter::printResult("Cancel Invoice", "Invoice", $invoice->getId(), $notify, null);