<?php
use Microsoft\Graph\Beta\GraphServiceClient;
use Microsoft\Graph\Beta\Generated\IdentityGovernance\EntitlementManagement\AccessPackageAssignmentRequests\Item\Cancel\CancelPostRequestBody;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new CancelPostRequestBody();
$additionalData = [
'id' => 'request-id',
'requestStatus' => 'cancelled',
];
$requestBody->setAdditionalData($additionalData);
$graphServiceClient->identityGovernance()->entitlementManagement()->accessPackageAssignmentRequests()->byAccessPackageAssignmentRequestId('accessPackageAssignmentRequest-id')->cancel()->post($requestBody)->wait();