Problem with login/register

<?php

    $servername = "mysql-xxnorxx.alwaysdata.net";
    $username = "xxnorxx";
    $password = "*****";
    $dbName = "xxnorxx_testdb";

    $user_username = $_POST["usernamePost"];
    $user_password = $_POST["passwordPost"];

    //Make Connection
    $conn = new mysqli($servername, $username, $password, $dbName);
    //Check Connection
    if(!$conn)
    {
        die("Connection Faled.". mysqli_connect_error());
    }
    //else echo("Connection Success");

    $sql = "SELECT password FROM users WHERE username = '".$user_username."' ";
    $result = mysqli_query($conn, $sql);


    //Get the result and confirm login
    if (mysqli_num_rows($result) > 0)
    {
        //show data for each row
        while($row = mysqli_fetch_assoc($result))
        {
            if($row['password'] == $user_password)
            {
                echo "Login success";
            }
            else
            {
                echo "Password incorrect";
            }
        }
    }
    else
    {
        echo "user not found";
    }

?>