Try this code:
<?php
ini_set('display_errors', 'On');
error_reporting(E_ALL);
// Generate random amount between 28.00 and 30.00
$ran1 = mt_rand(2800, 3000);
$ran2 = $ran1/100;
// Config
$sAPIKey = ""; // private key
$sAPISecret = ""; // api secret
$sPair = "GLD_BTC";
$sRate = "0.0001";
$sNonce = time();
$sRequest = "https://www.tradesatoshi.com/api/private/submitorder";
$ch = curl_init();
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
// disable cert validation
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
$rParam = array('Market' => $sPair, 'Type' => 'Buy', 'Amount' => $ran2, 'Price' => $sRate);
$rParam = json_encode($rParam);
$rSignature = $sAPIKey . 'POST' . strtolower(urlencode($sRequest)) . $sNonce . base64_encode($rParam);
$hmac_sign = base64_encode(hash_hmac('sha512', $rSignature, base64_decode($sAPISecret), true));
$header = 'Basic ' . $sAPIKey . ':' . $hmac_sign . ':' . $sNonce;
$headers = array("Content-Type: application/json; charset=utf-8", "Authorization: $header");
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt($ch, CURLOPT_URL, $sRequest);
curl_setopt($ch, CURLOPT_POSTFIELDS, $rParam);
// run the query
$execResult = curl_exec($ch);
var_dump($execResult);
BTC Address
BTC: 1EjmkQq7pHsmKhhrpP3hcGehq3ryAF3Qrb