antares-cab/controllers/PayController.php

<?php

namespace app\controllers;

use Yii;
use app\models\PayForm;

class PayController extends \yii\web\Controller
{
    public function actionIndex()
    {
        $model = new PayForm();
        if ($model->load(Yii::$app->request->post())) {
            Yii::$app->session->setFlash('success', 'This is the message');

            return $this->refresh();
        }

        $cc = $model->getAmount();

        return $this->render('index', [
            'model' => $model,
        ]);
    }

}