AJAX check for uniqueness of YII2 username does not work. Can you tell me what's wrong in the code?

Question

JavaScript

Model rules:

public function rules()
    {
        return [
            [['username', 'password_hash', 'status'], 'required'],
            ['username', 'unique'],
            ['password_hash', 'string', 'min' => 6, 'max' => 255],
            [['auth_key'], 'string', 'max' => 32],
            ['status', 'in','range' => [
                User::STATUS_ACTIVE,
                User::STATUS_NOT_ACTIVE,
            ]]
        ];
    }
}

controller action

public function actionReg()
    {
        $model = new RegForm();
        
        if (Yii::$app->request->isAjax && $model->load(Yii::$app->request->post())) {
            Yii::$app->response->format = 'json';
            return \yii\widgets\ActiveForm::validate($model);
        }
        if($model->load(Yii::$app->request->post()) && $model->validate()){
            if($user = $model->reg()){
                if($user->status === User::STATUS_ACTIVE){
                    if(Yii::$app->getUser()->login($user)){
                        return $this->goHome();
                    }
                }
            }else{
                echo '<pre>';
                Yii::$app->session->setFlash('error','Возникла ошибка при регистрации');
                Yii::error('Возникла ошибка при регистрации');
                return $this->refresh();
            }
        }
        
        return $this->render('reg',
            ['model' => $model]
                );
    }

View:

<?php $form = ActiveForm::begin(['id' => 'registration-form',])?>

        <?= $form->field($model, 'username',['enableAjaxValidation' => true]) ?>

        <?= $form->field($model, 'password_hash')->passwordInput() ?>
    
        <?= $form->field($model, 'password_repeat')->passwordInput() ?>
    
        <?= $form->field($model, 'status')->hiddenInput()?>

        <div class="form-group">
            <div>
                <?= Html::submitButton('Зарегистрироваться', ['class' => 'btn btn-primary', 'name' => 'login-button']) ?>
            </div>
        </div>

    <?php ActiveForm::end(); ?>

Answer 1

no, that's not the point... we set it to only one field, and if we add it to the widget, then the whole field, but it doesn't work either...
figured out: ['username', 'unique'] - it works only with ActiveRecord attributes. And I have class RegForm extends Model.
Changed: ['username', 'ajaxValidate'],
public function ajaxValidate($attribute)
{
$user = User::findOne(['username' => $this->username]);
if($user){
$this->addError($attribute, 'User with such login exists');
}elseif (!preg_match('/\+\d{12,15}/', $this->username)) {
$this->addError($attribute, 'Enter your phone number in the format [phone]');

Answer 2

For ajax validation to work, you need to enable it when displaying the form widget.

<?php 
$form = ActiveForm::begin([
'id' => 'registration-form',
'enableAjaxValidation' => true,
])
?>

You should also check the url where the form is sent and it is possible to specify it explicitly in the widget config. I will add that you can specify not only the send url, but also the url for ajax validation, they can be different actions.