<?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([ ]);
$additionalData = [
'user@odata.bind' => 'https://graph.microsoft.com/beta/users/24b3819b-4e1d-4f3e-86bd-e42b54d0b2b4',
];
$requestBody->setAdditionalData($additionalData);
$result = $graphServiceClient->teams()->byTeamId('team-id')->channels()->byChannelId('channel-id')->members()->post($requestBody)->wait();