In previous Adwords API version i was able to do:
$adWordsServices = new AdWordsServices();
$manageCustomerService = $adWordsServices->get($session, ManagedCustomerService::class);
$selector = new PendingInvitationSelector(array($session->getClientCustomerId()));
$pending = $manageCustomerService->getPendingInvitations($selector);
Please let me know how to do the same in new Ads API