问人脸检测提示parsing error - check content-type and body？

https://service.image.myqcloud.com/face/detect

method:POST

Host: service.image.myqcloud.com

Authorization: '.$Authorization.'

Content-Type:application/json

curl_setopt($ch, CURLOPT_POSTFIELDS, $data);

$data内容如下：{"appid":"1251436815","mode":1,"url":"http:\/\/file.001pp.com\/clip\/ueditor\/asp\/upload\/image\/20180621\/15295731301532804.png"}

一直提示：{"code":3,"message":"invalid request: parsing error - check content-type and body","data":{}}