mysqli_error() expects exactly 1 parameter, 0 given in

Warning: mysqli_error() expects exactly 1 parameter, 0 given in D:\wamp64\www\ygeshopok\mycart-inc.php on line 339
插入失败:

break;
/*第4步提交订单，并反馈订单信息，
此时变量$action的值为"ok",$action的值来自第3步的表单*/
case "ok":
$username=$_POST['username'];
date_default_timezone_set('Asia/Shanghai'); //设置系统时区为本地时区
$actiondate=date("Y-m-d H:i:s");
$dingdan=date("YmdHis");
$youbian=$_POST['youbian'];
$fapiaotaitou=$_POST['liuyan'];
$zhifufangshi=$_POST['zhifufangshi'];
$songhuofangshi=$_POST['songhuofangshi'];
$shousex=$_POST['shousex'];
$zonger=$_POST['zonger'];
$realname=$_POST['userzhenshiname'];
$useremail=$_POST['useremail'];
$usertel=$_POST['usertel'];
$fahuofeiyong=$_POST['fahuofeiyong'];
$fapiao=$_POST['fapiao'];
$shouhuodizhi=$_POST['shouhuodizhi'];
include ('db_fns.php');
foreach ($_SESSION['cart'] as $GoodID => $qty)  { 
  $sumPrice3=0;
  $sumPrice3=$sumPrice3+$qty*get_Good_Price($GoodID);
  $goodname=get_Good_Name($GoodID);
  $price=get_Good_Price($GoodID);  
include "conn.php";
$myquery="insert into orders(username,actiondate,goodid,goodname,bookcount,dingdan,zhuangtai,youbian,fapiaotaitou,zhifufangshi,songhuofangshi,shousex,xiaoji,zonger,userzhenshiname,useremail,usertel,danjia,fahuofeiyong,fapiao,shouhuodizhi) values('".$username."','".$actiondate."',".$GoodID.",'".$goodname."',".$qty.",'".$dingdan."',0,'".$youbian."','".$fapiaotaitou."',".$zhifufangshi.",".$songhuofangshi.",".$shousex.",".$sumPrice3.",".$zonger.",'".$realname."','".$useremail."','".$usertel."',".$price.",".$fahuofeiyong.",".$fapiao.",'".$shouhuodizhi."')";  //设定插入语句
$result=mysqli_query($lnk,$myquery) or die("<br>插入失败: " . mysqli_error());  //执行插入sql语句
//mysqli_free_result($result);
mysqli_close();
}

需要提供一个参数给某个函数，但是代码里面没给

mysqli_error得有一个参数，就是你连接数据库