title: Bittrex API request
body: <p>I'm trying to get my wallet balance with the bittrex API and i don't understand why the code provided by bittrex documentation doesn't work :</p>
  
  <pre><code>$apikey = 'xxx';
  $apisecret = 'xxx';
  $nonce = time();
  $uri = 'https://bittrex.com/api/v1.1/market/getopenorders?apikey=' .
      $apikey . '&amp;nonce=' . $nonce;
  $sign = hash_hmac('sha512', $uri, $apisecret);
  $ch = curl_init($uri);
  curl_setopt($ch, CURLOPT_HTTPHEADER, array('apisign:' . $sign));
  $execResult = curl_exec($ch);
  $obj = json_decode($execResult);
  </code></pre>
  
  <p>The <code>curl_exec</code> function returns false, i don't understand why.
  Thank for your help !</p>