mysqli update query using ajax in wordpress theme

我正在开发一个基于 wordpress 的应用程序，我需要使用 ajax 更改所列订单的状态。下面的代码给了我以下错误：无法加载资源：服务器以状态 500 响应（内部服务器错误）

我不知道为什么这不起作用。请帮帮我。

.HTML：

<select id="status-<?php echo $order_id[$xx]; ?>" name="status-<?php echo $order_id[$xx]; ?>" onChange="return statuschange(this, '<?php echo $order_id[$xx]; ?>');">
    <option value="0"<?php if ($status_code[$xx] == 0){ echo' selected="selected"'; }; ?>>incoming</option>
    <option value="1"<?php if ($status_code[$xx] == 1){ echo' selected="selected"'; }; ?>>processing</option>
    <option value="2"<?php if ($status_code[$xx] == 2){ echo' selected="selected"'; }; ?>>processed</option>
    <option value="3"<?php if ($status_code[$xx] == 3){ echo' selected="selected"'; }; ?>>packing</option>
    <option value="4"<?php if ($status_code[$xx] == 4){ echo' selected="selected"'; }; ?>>ready</option>
    <option value="5"<?php if ($status_code[$xx] == 5){ echo' selected="selected"'; }; ?>>posted</option>
    <option value="6"<?php if ($status_code[$xx] == 6){ echo' selected="selected"'; }; ?>>received</option>
    <option value="7"<?php if ($status_code[$xx] == 7){ echo' selected="selected"'; }; ?>>returned</option>
    <option value="8"<?php if ($status_code[$xx] == 8){ echo' selected="selected"'; }; ?>>deleted</option>
</select>

JS（在上述HTML代码所在的文件末尾）：

function statuschange(element, orderid){
    var oldValue = element.defaultValue;
    var newValue = element.value;
    var admincomment = prompt("Change order status?'n'nAdd comment:", "");
    if (admincomment != null) {
        var newValueecn = encodeURI(newValue);
        var admincommentenc = encodeURI(admincomment);
        var orderidenc = encodeURI(orderid);
        if (window.XMLHttpRequest) { 
            xmlhttp = new XMLHttpRequest();
            xmlhttp.onreadystatechange = function () { if (xmlhttp.readyState == 4 && xmlhttp.status == 200) { element.defaultValue = newValue; location.reload(true); console.log(xmlhttp.responseText); } }
            xmlhttp.open("GET", "http://www.mydomain.tld/wp-content/themes/mycustomtheme/changestatus.php?newstatusz=" + newValueecn + "&comment=" + admincommentenc + "&orderid=" + orderidenc, true);
            xmlhttp.send(); }
        } else {
        element.value = element.defaultValue; } };

PHP （changestatus.php）：

function cleaninput($input){
    $input = trim($input);
    $input = stripslashes($input);
    $input = htmlspecialchars($input);
    return $input;
}
if(isset($_GET['newstatusz'])){
    $newstatusz = cleaninput($_GET['newstatusz']);
} else { exit; }
if(isset($_GET['comment'])){
    $comment = cleaninput($_GET['comment']);
} else { exit; }
if(isset($_GET['orderid'])){
    $orderid = cleaninput($_GET['orderid']);
} else { exit; }
$current_user = wp_get_current_user();
$userloggedin = $current_user->user_login;
$mysqli1 = new mysqli("localhost", "myuser", "mypass", "mydatabase");
if ($mysqli1->connect_error){ die("DB connect error: " . $mysqli1->connect_error); };
$mysqli1->set_charset("utf8");
$newstatusz = $mysqli1->real_escape_string($newstatusz);
$userloggedin = $mysqli1->real_escape_string($userloggedin);
$comment = $mysqli1->real_escape_string($comment);
$mysqli1->query("UPDATE poszter_admin SET statusz_kod = '$newstatusz', user = '$userloggedin', comment = '$comment' WHERE order_id = '$orderid'");
$mysqli1->close();
exit;