Google 的 Safe Browsing 接口是不是挂掉了

https://developers.google.com/safe-browsing/v4/lookup-api

Google 提供的检测网址安全性的接口，不过按照文档 curl 返回的 json 是空的，又用 Stackoverflow 上看到的代码测试了，返回的也是空的。是我姿势不对嘛？

附代码：

<?php
$url = 'https://v2ex.com';


$apiKey = 'YOUR API KEY';
$apiUrl = 'https://safebrowsing.googleapis.com/v4/threatMatches:find?key='.$apiKey;

$params = [
    'client' => [
        'clientId' => 'foobar',
        'clientVersion' => '1.2.3'
    ],
    'threatInfo' => [
           "threatTypes" =>["MALWARE", "SOCIAL_ENGINEERING"],
          "platformTypes" => ["WINDOWS"],
           'threatEntryTypes' => ['URL'],
        'threatEntries' => [
            [ 'url' => $url ]
        ]
    ]
];


$ch = curl_init($apiUrl);
curl_setopt_array($ch, [
    CURLOPT_POST => 1,
    CURLOPT_RETURNTRANSFER => 1,
    CURLOPT_HEADER => 1,
    CURLOPT_POSTFIELDS => json_encode($params),
    CURLOPT_HTTPHEADER => [
        'Content-Type: text/json'
    ]
]);

$res = curl_exec($ch);
?> <pre><?php echo print_r($res, true); ?></pre> <?php
?>