为什么我的活动不在octobercms工作?

I am trying to wrap my head around octobercms group and permission. I added a great plugin on permission and role that is straight forward and easy to implement on page/users but my question is do I have to add all users to group manually from the backend like one by one?

I created a new plugin and in the Plugin.php file I have this, use Event; //on the top of the file

I have this in its boot method to add users to the group with code seller on registration.

    public function boot()
{

Event::listen('rainlab.user.register', function($user){
    $group = 
    \Rainlab\User\Models\UserGroup::where('code', 'seller')->first();

    $user->groups()->add($group);
    $user->save();
});

Doesn't seem to work. what am I missing in all of these?

plugin.php file

<?php namespace Corymillz\Newplug;

use System\Classes\PluginBase;
use Event;

class Plugin extends PluginBase
{
   public function registerComponents()
    {
    }

    public function registerSettings()
    {
    }

   public function boot()
{ 

Event::listen('rainlab.user.register', function($user,$postdata){
    $group = \Rainlab\User\Models\UserGroup::where('code', 'seller')->first();

    $user->groups = $group->id;
    $user->save();
});


}

}

just change your code like that.

Event::listen('rainlab.user.register', function($user,$postdata){
    $group = \Rainlab\User\Models\UserGroup::where('code', 'seller')->first();

    $user->groups = $group->id;
    $user->save();
});