What's wrong with insert via PHP in MySQL?

PHP:

<?php

$mysql = mysqli_connect('localhost', 'p927805w_mdmaa', 'flinttyk123', 'p927805w_mdmaa');
if (!$mysql) exit('[CONNECTION ERROR]');

if ($stmt = $mysql->prepare('INSERT INTO `test` (`nickn`) VALUES ($_POST['nickn'])')) {
$nickn = (isset($_POST['nickn']) ? strval($_POST['nickn']) : '$nickn');
$stmt->bind_param('ss', $nickn);
if ($stmt->execute()) {
echo 'data received, inserting...';
$stmt->close();
} else {
echo 'error';
$stmt->close();
}
}
?>

PHP

<?php



$mysql = mysqli_connect('localhost', 'p927805w_mdmaa', 'flinttyk123', 'p927805w_mdmaa');

if (!$mysql) exit('[CONNECTION ERROR]');



if ($stmt = $mysql->prepare('INSERT INTO `test` (`nickn`) VALUES ($_POST['nickn'])')) {

    $nickn = (isset($_POST['nickn']) ? strval($_POST['nickn']) : '$nickn');

    $stmt->bind_param('ss', $nickn);

    if ($stmt->execute()) {

        echo 'data received, inserting...';

        $stmt->close();

    } else {

        echo 'error';

        $stmt->close();

    }

}

?>

переменная nickn передается по POST - запросу из Lua скрипта
нужно записать текст, а оно записывает так:



т.е пустое значение, а должно записать:
nickname=ник из сампа
в консоли Moonloader'a:

DATA [ML] (script) test.lua: nickname=DieDoS
RESPONSE [ML] (script) test.lua: data received, inserting...
CODE [ML] (script) test.lua: 200
HEADERS [ML] (script) test.lua: table: 0x0ef05f10
STATUS [ML] (script) test.lua: HTTP/1.1 200 OK