Постоянно 404 страница (главная страница) [дубликат]

Не могу разобраться в связи с чем постоянно на главной странице 404 PAGE пишется, вместо HELLO GUEST или просто INDEX (если авторизован пользователь) В самом файле library\main.php:

function getUrlSegment($num){
    $url = strtolower($_GET['url']);
    $urlSegments = explode('/',$url);
    return $urlSegments[$num];
}

На главной странице:

<?php
ini_set('error_reporting', E_ALL);
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
session_start();
require_once 'core/library/db.php';
require_once 'core/configs/main.php';
require_once 'core/library/main.php';
require_once 'core/library/validator.php';
require_once 'core/models/category.php';
require_once 'core/models/post.php';
//$url = (isset($_GET['$url']) ? $_GET['$url'] : 0);
$cntrName = (is_null(getUrlSegment(0))) ? 'main' : getUrlSegment(0);
$actionName = (is_null(getUrlSegment(1))) ? 'action_index' : 'action_'.getUrlSegment(1);
if(file_exists('core/controllers/'.$cntrName.'.php')){
    require_once 'core/controllers/'.$cntrName.'.php';
    if(function_exists($actionName)){
        $actionName();
    }else{
        show404page();
    }
}else {
    show404page();
}

В контроеллере:

    <?php
    function action_index(){
        if(is_auth()){
            echo 'INDEX PAGE';
        }else{
            echo 'Hello guest!';
        }
}
    function action_contact(){
    echo 'CONTACT PAGE';
}
    function action_registration(){
        if($_SERVER['REQUEST_METHOD'] == 'POST'){
            $formData = [
                'login' => getSaveData(htmlspecialchars(trim($_POST['login']))),
                'password' => getSaveData(trim($_POST['password'])),
                'email' => getSaveData(trim($_POST['email']))
            ];
            $rules = [
                'login' => ['required', 'login'],
                'password' => ['required','password'],
                'email' => ['required','email']
            ];
            $errors = validateForm($rules, $formData);
            if(empty($errors)){
                $formData['password'] = md5($formData['password'].SECRET_KEY);
            //$sql = "INSERT INTO `user` (`login`, `password`, `email`) VALUES ('{$formData['login']}','{$formData['password']}','{$formData['email']}') ON DUPLICATE KEY UPDATE login='{$formData['login']}', password='{$formData['password']}', email='{$formData['email']}'";
            $sql = "INSERT INTO `user`(`login`, `password`, `email`) VALUES ('{$formData['login']}','{$formData['password']}','{$formData['email']}')";
            $sql1 = "SELECT id FROM user WHERE login='{$formData['login']}' or email='{$formData['email']}'";
            $res = selectData($sql1);
            if($res->num_rows === 0){
            }
            if(insertUpdateDelete($sql)) {
                header("Location: /main/successReg");
            }else{
                    echo 'Пользователь с таким логином или почтой уже существует. :(';
                }
            }
        }
        renderView('registration');
    }
    function action_successReg(){
        echo 'Поздравляем!';
    }
    function action_login()
    {
        if ($_SERVER['REQUEST_METHOD'] == 'POST') {
            $formData = [
                'login' => getSaveData(htmlspecialchars(trim($_POST['login']))),
                'password' => getSaveData(trim($_POST['password'])),
            ];
            $formData['password'] = md5($formData['password'] . SECRET_KEY);
            $sql = "SELECT id FROM user WHERE login='{$formData['login']}' and password='{$formData['password']}'";
            $res = selectData($sql);
            if ($res->num_rows === 0) {
                echo 'Некоректный логин или пароль!';
            } else {
                $_SESSION['user'] = mysqli_fetch_assoc($res);
                header('Location: /');
            }
        }
        renderView('login', []);
    }
    function action_logout(){
        session_unset();
        session_destroy();
        header('Location: /');
    }