$url = "https://api.binance.com/api/v3/userDataStream";
$sPD = "";
$clength = strlen($sPD);
$aHTTP = array(
'http' =>
array(
'method' => 'POST',
'header' => 'X-MBX-APIKEY: '.$akey,
'content' => $sPD
)
);
$context = stream_context_create($aHTTP);
$contents = file_get_contents($url, false, $context);
$listenkey = json_decode($contents)->listenKey;