Laravel 5 subdomain Route shows 'server not found'

Want to show usernames as subdomain like :

user1.domain.com , user2.domain.com etc...

where 'user1' and 'user2 ' are just username saved in database.

web.php :

Route::group(['domain' => '{subdomain}.my-domain-name.com'], function ($sub) {
    echo $sub;
});

I visited example.my-domain.com which shows

NB : Using Laravel 5.4

via Chebli Mohamed