我试着连接MQTTS和我的HTTPS服务器，但它不工作。它在MQTTX上工作正常，但与PHP它不连接。

<?php 

$server   = 'myServer';
$port     = '8883';
$clientId = 'testing';
$username = 'XXXX';
$password = 'XXXX';
$clean_session = false;

$connectionSettings  = new ConnectionSettings();
$connectionSettings->setUsername($username)
    ->setPassword($password)
    ->setKeepAliveInterval(60)
    ->setLastWillTopic('mytopic')
    ->setLastWillMessage('client disconnect')
    ->setLastWillQualityOfService(1);

$mqtt = new MqttClient($server, $port, $clientId);
$mqtt->connect($connectionSettings, $clean_session);

$mqtt->subscribe('mytopic/respond', function ($topic, $message) use ($mqtt) {
    echo $message;
}, 2);

$mqtt->close();
$mqtt->interrupt();
?>

如何连接MQTTS和PHP。