API,JSON什么都不返回

coud anyone of you tell me what I'am doing wrong? I use sample code from API documentation(https://github.com/bitmarket-net/api). JSON returning nothing. I only add echo bitmarket_api("info");and replace public and private keys ( $key $secret ).

<html>
<body>
<?php
function bitmarket_api($method, $params = array())
{
$key = "xxxxxxxxx";
$secret = "xxxxxxxxx";

$params["method"] = $method;
$params["tonce"] = time();

$post = http_build_query($params, "", "&");
$sign = hash_hmac("sha512", $post, $secret);
$headers = array(
    "API-Key: " . $key,
    "API-Hash: " . $sign,
);

$curl = curl_init();
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_URL, "https://www.bitmarket.pl/api2/");
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, $post);
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
$ret = curl_exec($curl);

return json_decode($ret);
}

  echo  bitmarket_api("info"); // line 30

?>
</body>   
</html>

edit After solve SSL problem function returning true, and I have error ' Catchable fatal error: Object of class stdClass could not be converted to string in C:\xampp\htdocs\index1.php on line 30'

edit Solved. I create new object and adding echo into metod.Thank you all for help :)

Write

echo bitmarket_api("info") ? "TRUE" : "FALSE";

and you will see if something is returned