bitmex post order error PHP bot

Question

我正在用PHP创建一个bitmex bot。

我成功取得了钱包余额。

但是无法发布新订单，它显示签名无效错误。

bitmex网站上没有可用的PHP文档。

感谢任何帮助。

这是我正在使用的代码

$apiKey = "L5kwGvrsX-3FFsPtpO4jhXu9";
        $apiSecret = "OCFCnv6M2jbz-S9vioj5Ytoyjyk5dPyrkY87ecmUDh74F_6V";
        $expires = strtotime("+1 minutes");
        $verb = "POST";
        $path ="/api/v1/order";
        $data = array('symbol' => 'XBTUSD','side'=>'Buy','orderQty'=>'100','ordType'=>'Market','timeInForce'=>'GoodTillCancel');
        $data_json = json_encode($data);
        $string = $verb.$path.(string)$expires.$data_json;
        $sign = bin2hex(hash_hmac('sha256', $string, $apiSecret)); 
        $ch = curl_init();

        curl_setopt($ch, CURLOPT_HTTPHEADER,array(
   "Content-Type : application/x-www-form-urlencoded",
   "Accept : application/json",
  "X-Requested-With: XMLHttpRequest",
  "api-expires:".$expires,
  "api-key: ".$apiKey,
  "api-signature:".$sign
));
        curl_setopt($ch, CURLOPT_VERBOSE, true);
        curl_setopt($ch, CURLOPT_URL,"https://testnet.bitmex.com/api/v1/order");
        curl_setopt($ch, CURLOPT_POST, 1);
        curl_setopt($ch, CURLOPT_POSTFIELDS,
                    $data);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        $server_output = curl_exec ($ch);
        $information = curl_getinfo($ch, CURLINFO_HTTP_CODE);
        print_r($information);
        print_r($server_output);
        curl_close ($ch);