<?php
use Microsoft\Graph\Beta\GraphServiceClient;
use Microsoft\Graph\Beta\Generated\Models\AadUserConversationMember;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new AadUserConversationMember();
$requestBody->setOdataType('#microsoft.graph.aadUserConversationMember');
$requestBody->setRoles(['owner', ]);
$requestBody->setTenantId('4dc1fe35-8ac6-4f0d-904a-7ebcd364bea1');
$additionalData = [
'user@odata.bind' => 'https://graph.microsoft.com/beta/users/82af01c5-f7cc-4a2e-a728-3a5df21afd9d',
];
$requestBody->setAdditionalData($additionalData);
$result = $graphServiceClient->chats()->byChatId('chat-id')->members()->post($requestBody)->wait();