like.php

<?php
session_start();
$postid = $_POST['postid'];
$userid = $_SESSION['id'];
$conn = mysqli_connect('localhost', 'root', '', 'maksitwitter');
if (!$conn) {
    die('Connection failed: ' . mysqli_connect_error());
}
$liked = mysqli_query($conn, "SELECT * FROM post_likes WHERE post_id = '$postid' AND user_id = '$userid'");
if ($liked && mysqli_num_rows($liked) > 0) {    
    echo 'liked';
    exit;
}
$query = "UPDATE posts SET likes = likes + 1 WHERE id = '$postid'";
$query2 = "INSERT INTO post_likes (post_id, user_id) VALUES ('$postid', '$userid')";
mysqli_query($conn, $query2);
if (mysqli_query($conn, $query)) {
    mysqli_close($conn);
    echo 'success';
} else {
    echo 'Error: ' . mysqli_error($conn);
}
?>