<?php
use Microsoft\Graph\Beta\GraphServiceClient;
use Microsoft\Graph\Beta\Generated\Models\ReferenceCreate;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new ReferenceCreate();
$requestBody->setOdataId('https://graph.microsoft.com/beta/groups/c0a74b4d-2694-4d5d-a964-1bee4ff0aaf2');
$graphServiceClient->identityGovernance()->entitlementManagement()->accessPackages()->byAccessPackageId('accessPackage-id')->incompatibleGroups()->ref()->post($requestBody)->wait();