How to fix The requested URL was not found on this server error for the hello/name url?

RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ index.php [QSA,L]

<?php 

require __DIR__ . '/vendor/autoload.php';
date_default_timezone_set ( "America/New_York" );

// $log = new Monolog\Logger('name');
// $log->pushHandler(new Monolog\Handler\StreamHandler('app.log', Monolog\Logger::WARNING));
// $log->addWarning('Foo');

$app = new \Slim\Slim();
$app->get('/hello/:name', function ($name) {
    echo "Hello, $name";
});
$app->run();

?>

RewriteBase /Applications/MAMP/htdocs/SimplePHPWebsite/

$app->get('/', function() {
    echo 'Hello, this is the homepage.';
});

$app->get('/contact', function() {
    echo 'contact us.';
});