Active Form Ajax Validation

if (Yii::$app->request->isAjax) {
    $model->load($_POST);
    Yii::$app->response->format = Response::FORMAT_JSON;
    return ActiveForm::validate($model);
} elseif ($model->load($_POST) && $model->save()) {
    return $this->redirect(['view', 'id' => $model['id']]);
} else {
    return $this->render('update', [
        'model' => $model
    ]);
}

<?php echo $form->field($model,'value')->begin(); ?>
 
<?php echo Html::activeLabel($model,'value'); ?>
<?php echo Html::activeTextInput($model,'value', ['maxlength'=>255, 'placeholder' => '123.456.78.9']); ?>
<?php echo Html::error($model,'value', ['class' => 'help-block']); ?>
 
<?php echo $form->field($model,'value')->end(); ?>