How to use curl to submit json format data in PHP

$data = array("name" => "Hagrid", "age" => "36");
$data_string = json_encode($data);

$ch = curl_init('http://api.local/rest/users');
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_POSTFIELDS,$data_string);
curl_setopt($ch, CURLOPT_RETURNTRANSFER,true);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Content-Type: application/json',
    'Content-Length: ' . strlen($data_string))
);
 
$result = curl_exec($ch);