Input::get('submit') tidak berfungsi

kenapa saat saya klik buttonnya tidak keluar hasil dari echo tersebut init.php sudah berfungsi saat di test di login.php seperti di tutorial ini <a href='https://www.sekolahkoding.com/kelas/sistem-login-dan-register-oop-php/video/register-user-GFn0X9TsUb'>https://www.sekolahkoding.com/kelas/sistem-login-dan-register-oop-php/video/register-user-GFn0X9TsUb</a>

register.php

<?php

require_once 'core/init.php';


if( Input::get('submit') ){
echo 'Halo';
}

?>
<form class="form-signin" method="post" action="register.php">

<h1 class="h3 mt-5 mb-3 font-weight-normal">Please Register</h1>
<label for="inputEmail" class="sr-only">Email address</label>

<input type="text" id="inputEmail" class="form-control mb-3" placeholder="Username" autofocus="" name="username">

<label for="inputPassword" class="sr-only">Password</label>

<input type="password" id="inputPassword" class="form-control mb-3" placeholder="Password" name="password">

<button class="btn btn-lg btn-primary btn-block" type="submit" name="submit">Register</button>

</form>

input.php

 <?php

	class Input{

		public static function get($name)
		{
			if( isset($_POST[$name]) )
			{
				return $_POST[$name];
			}
			else if( isset($_GET[$name]) )
			{
				return $_GET[$name];
			}
			return false;
		}
	}

?>

init.php

<?php

	session_start();

	//load kelas
	spl_autoload_register(function($class){

		require_once 'classes/' .$class. '.php';

	});

?>