调用Originality.ai AI检测API返回invalid api call错误的问题排查求助

各位大佬好，我最近在尝试调用Originality.ai的AI检测API，但是一直收到"invalid api call"的错误提示，实在找不到问题出在哪，想请大家帮忙排查下。

下面是我写的PHP代码：

function originlaity_ai()
{
    $ch = curl_init();

    curl_setopt($ch, CURLOPT_URL, 'https://api.originality.ai/api/v1//scan/ai');
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, '{\"content\": \"A delicious cup of tea is a simple and timeless pleasure, and for many people its even more than that...\"}');

    $headers = array();
    $headers[] = 'Content-Type: application/json';
    $headers[] = 'X-OAI-API-KEY: XXXXXXXXXXX';
    curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

    $result = curl_exec($ch);
    if (curl_errno($ch)) {
        echo 'Error:' . curl_error($ch);
    }
    var_dump($result);
    curl_close($ch);
}

originlaity_ai();

我对照了官方文档的要求，文档内容如下：

Making Requests

In order to use our API you'll need to create an API key on the "My Keys" table on the left or click this button:
To start making requests: Create a header key named X-OAI-API-KEY and use your api key as the value in your application of choice

Main Endpoint:
https://api.originality.ai/api/v1

All Request responses are returned in JSON

AI Detection
[POST]
/scan/ai

Run an AI Detection scan for a full piece of content

Request Example:
{
"content": "A delicious cup of tea is a simple and timeless pleasure, and for many people it's even more than that..."
}

我已经确认API密钥是正确的，也按照要求设置了Content-Type为application/json，但还是报错。有没有朋友能帮我看看代码里哪里有问题？比如URL的格式、POST数据的转义之类的？

备注：内容来源于stack exchange，提问作者Steve