答得好
对于使用curl的多部分过帐，您需要使用如下标题
第一个
对于您的情况，只需将"Content-Type:multipart/form-data"添加到函数中即可

$postData = array();
$postData["Answer"] = $text;

foreach ($images as $index => $file) {
    $postData['Files[' . $index . ']'] = curl_file_create(
        $file,
        $functions->mime_type($file),
        pathinfo($file, PATHINFO_FILENAME)
    );
}

$ch = curl_init();
curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
curl_setopt($ch, CURLOPT_USERPWD, $user . ":" . $password); 
curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type:multipart/form-data",'merchantId:98765431')); //HERE THE ADD
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $postData);
curl_setopt($ch ,CURLOPT_URL ,"https://...");
$response = curl_exec($ch);