<div class="container message_form">

            <?php

            if( Yii::$app->session->hasFlash('success')): ?>
                <div class="container1" style="position: relative">
                    <div class="alert alert-success alert-dismissible" role="alert">
                        <button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">&times;</span></button>
                        <?php echo Yii::$app->session->getFlash('success'); ?>
                    </div>
                </div>
            <?php endif;?>

            <?php if( Yii::$app->session->hasFlash('error')): ?>
                <div class="container1" style="position: relative;">
                    <div class="alert alert-danger alert-dismissible" role="alert">
                        <button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">&times;</span></button>
                        <?php echo Yii::$app->session->getFlash('error'); ?>
                    </div>
                </div>
            <?php endif; ?>

        </div>

$contact_left = new FormLeft();
    if (Yii::$app->request->isAjax){
        if($contact_left->load(Yii::$app->request->post())){
            Yii::$app->session->setFlash('success', 'Дякуємо за вашу заявку, ми звяжемся з вами найблищим часом');
            return 'Запрос принят!';
        }
    }

$('#form-left').on('beforeSubmit', function(){
    var data = $(this).serialize();
    $.ajax({
        url: '/site/index',
        type: 'POST',
        data: data,
        success: function(res){
            console.log(res);
        },
        error: function(){
            alert('Error!');
        }
    });
    return false;
});