Как загрузить файл VK API PHP 7+Curl?

<?php
$params=[
'access_token'=>"",
'group_id'=>"82346155",
'v'=>"5.69"
];

$url = "https://api.vk.com/method/photos.getWallUploadServer?" .http_build_query($params);

$res=json_decode(file_get_contents($url),true);
$upload_url = $res['response']['upload_url'];


$data = array('photo' => new CURLFile('maxresdefault.jpg'));

$ch = curl_init();

print_r($data);

curl_setopt_array($ch, [
CURLOPT_POSTFIELDS => $data,
CURLOPT_URL => $upload_url,
CURLOPT_POST => 1, 
CURLOPT_RETURNTRANSFER => 1,
]);
$curl_result = json_decode(curl_exec($ch));
print_r($curl_result);
curl_close($ch);


?>

Array
(
    [photo] => CURLFile Object
        (
            [name] => maxresdefault.jpg
            [mime] => 
            [postname] => 
        )

)
stdClass Object
(
    [server] => 639631
    [photo] => []
    [hash] => 5afc43f8882484fb754ef37413847fba
)