登录页面未使用mySQL数据库类进行验证

Question

问题是，每次我尝试使用用户名和密码验证时，我得到的都是该页面不起作用，并且当前无法处理此请求。

我试图通过将其链接到我的数据库类来备份它，但是它没有起作用。

login.php类：

    <?php
    session_start();
    $username = $_POST['Username'];
    $password = $_POST['Password'];
    $host = "example.ac.uk";
    $user = "example";
    $pass = "exampleeea";
    $db = "example";

    $_SESSION['Username'] = $username;
    $_SESSION['Password'] = $password;

    $link = new mysqli($host, $user, $pass, $db, 3306);

    if($link->connect_error){
        die("Connection failed:". $link->connect_error);
    } else{

    }


    $sql = "SELECT * FROM users WHERE Username = "". mysqli_real_escape_string($link, $username) . "" AND Password = "". mysqli_real_escape_string($link, $password).  " "";

    $result = mysqli_query($link, $sql);
    $row = mysqli_fetch_array($result);
    if($row['Username']== $username && $row ['Password'] == $password){
        header('Location: AddPost.html');

    } else {
        die("incorrect Username or Password");
    }
        $link ->close();

任何想法可能是什么问题？