Yii2 How to auto register new user without using site/signup - yii2

Question

I want to signup new user every time I add a new client. I do not want to manually register a new user using the web/site/signup form via the browser.
I am trying to auto register new users from ClientController and I am having no luck at all. No error returned, it is as if the code doesn't run at all.
I can easily register the same user through site controller at site/signup but can not at all auto register through another controller by calling SignupForm model. Please help
I have this in my client controller
namespace frontend\controllers;
use Yii;
use yii\web\Controller;
use yii\helpers\Html;
use frontend\models\Client;
use frontend\models\SignupForm;
class ClientController extends Controller
{
public function behaviors()
{
return [
'verbs' => [
'class' => VerbFilter::className(),
'actions' => [
'delete' => ['post'],
],
],
];
}
public function actionCreate()
{
$model = new Client;
if ($model->load(Yii::$app->request->post()))
{
$model->save();
$useremail = $model->Email;
$signupForm = new SignupForm();
$signupForm->username = $useremail;
$signupForm->password = $useremail;
$signupForm->email = $useremail;
$signupForm->created_at = time();
$signupForm->picture = null;
$signupForm->created_by = Yii::$app->session->get('USER_ID');
$NewUser = $signupForm->signup();
print_r($NewUser);
exit;
}
else{
return $this->render('create', [
'model' => $model
]);
}
}
}
and this is my SignupForm code:
<?php
namespace frontend\models;
use common\models\User;
use yii\base\Model;
use Yii;
/**
* Signup form
*/
class SignupForm extends Model
{
public $username;
public $email;
public $password;
public $picture;
public $created_by;
/**
* #inheritdoc
*/
public function rules()
{
return [
['username', 'filter', 'filter' => 'trim'],
['username', 'required'],
['username', 'unique', 'targetClass' => '\common\models\User', 'message' => 'This username has already been taken.'],
['username', 'string', 'min' => 2, 'max' => 255],
['email', 'filter', 'filter' => 'trim'],
['email', 'required'],
['email', 'email'],
['email', 'unique', 'targetClass' => '\common\models\User', 'message' => 'This email address has already been taken.'],
['password', 'required'],
['password', 'string', 'min' => 6],
[['picture'], 'string'],
[['picture'],'default', 'value'=>null],
[['created_by'], 'integer'],
[['created_by'], 'default', 'value'=>Yii::$app->session->get('USER_ID')],
];
}
/**
* Signs user up.
*
* #return User|null the saved model or null if saving fails
*/
public function signup()
{
$this->created_by = Yii::$app->session->get('USER_ID');
if ($this->validate()) {
$user = new User();
$user->username = $this->username;
$user->email = $this->email;
$user->setPassword($this->password);
$user->generateAuthKey();
$user->created_by = $this->created_by;
$user->picture = $this->picture;
//Save user
$user->save(false);
return $user;
}
return null;
}
}