<?php
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Graph\Generated\Models\ChatMessage;
use Microsoft\Graph\Generated\Models\ItemBody;
use Microsoft\Graph\Generated\Models\BodyType;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new ChatMessage();
$body = new ItemBody();
$body->setContentType(new BodyType('html'));
$body->setContent('<emoji alt=\"😶🌫️\"></emoji>');
$requestBody->setBody($body);
$result = $graphServiceClient->chats()->byChatId('chat-id')->messages()->post($requestBody)->wait();