PHP Authentication works only local - php

Question

I have a PHP login page that works perfectly locally, but when in server always come out with "Invalid Username or Password". I tried it in two different servers and the result was the same.
login.php
session_start(); // Starting Session
$error = ''; // Variable To Store Error Message
if (isset($_POST['submit'])) {
if (empty($_POST['username']) || empty($_POST['password']))
{
$error = "Username or Password is invalid";
}
else
{
// Define $username1 and $password1
$username1 = $_POST['username'];
$password1 = $_POST['password'];
include_once ('lib/db.php');
$connection = new mysqli($servername, $username, $password, $dbname);
$username1 = stripslashes($username1);
$password1 = stripslashes($password1);
$username1 = mysql_real_escape_string($username1);
$password1 = mysql_real_escape_string($password1);
// SQL query to fetch information of registerd users and finds user match.
$query = "select * from login where PASSWORD='$password1' AND USERNAME='$username1'";
$result = $connection->query($query);
$rows = mysqli_num_rows($result);
if ($rows == 1)
{
$_SESSION['user']=$username1; // Initializing Session
$_SESSION['pppv'] = 10;
header("Location: logged-in.php"); // Redirecting To Other Page
}
else
{
$error = "Username or Password is invalid";
}
}
}
EDIT
Try printing the query after submission gives me this:
Local:
select * from login where PASSWORD='test' AND USERNAME='test'
Server:
select * from login where PASSWORD='' AND USERNAME=''

Answer 1

Use isset($_POST['username']) ||isset($_POST['password'])instead of empty($_POST['username']) || empty($_POST['password']).
Read this to know the difference between isset and empty.

Answer 2

There's no context, but check these things:
Does your database contain the same credentials as local?
Does your requested page return http status such as 200? If it's 404, there's something wrong with your path's. If it's 500, there's an internal error (right permissions set?)
Did you check your log files?
Did you clear your browser cookies and history?
Did you print the full query (including filled parameters) to the window and did you execute this query in your database management tool? And did you get result?