将JRO从ANDROID传递给PHP无法正常工作

I am trying to pass set of product_ids from android to php and I need to store each product id in different rows accordingly.

Below is my JSON.

JSON

{
"product_ids": "[35, 31, 30]"
}

The number of product_ids would change based on the user.

Below is the android code used to pass product_ids JSON to PHP through HttpURLConnection

 protected String doInBackground(String... params) {

        try {

            URL url = new URL("http://myurl.com/r/jsontest.php");

            for(int i =0;i<list_productids.size();i++){
                try {
                    ob.put("product_ids",list_productids);
                     message = ob.toString();

                } catch (JSONException e) {
                    e.printStackTrace();
                }
                // mJSONArray.put(ob);
            }

            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setDoInput(true);
            conn.setDoOutput(true);
            conn.setUseCaches(false);
            conn.setRequestMethod("POST");
            conn.setReadTimeout( 10000 /*milliseconds*/ );
            conn.setConnectTimeout(15000 /* milliseconds */);
            conn.setRequestMethod("POST");
            conn.setDoInput(true);
            conn.setDoOutput(true);
            conn.setFixedLengthStreamingMode(message.getBytes().length);

            conn.setRequestProperty("Content-Type", "application/json;charset=utf-8");
            conn.setRequestProperty("Host", "xyz.com");



            //open
            conn.connect();

            //setup send
            os = new BufferedOutputStream(conn.getOutputStream());
            os.write(message.getBytes());
            //clean up
            os.flush();

            //do somehting with response
            is = conn.getInputStream();



        } catch (Exception ex) {
            ex.toString();
        }

        return null;
    }
}

PHP code as follows

<?php

include('config.php');
$msg = file_get_contents('php://input');
$input = json_decode($msg,true);
$rate = $input->{'product_ids'};
echo $msg;

$q = mysql_query("Insert into test(items) values ('$rate') ");
?>

SQL table is empty when I try to store the product_ids.

I am new to PHP, not sure where I am going wrong. Any help would be really greatfull.

Thanks.