Backend
Yii::$app->session->setFlash('success', "Your message to display.");
Frontend
<?php if (Yii::$app->session->hasFlash('success')): ?> <?= Yii::$app->session->getFlash('success') ?> <?php endif; ?>
Backend
Yii::$app->session->setFlash('success', "Your message to display.");
Frontend
<?php if (Yii::$app->session->hasFlash('success')): ?> <?= Yii::$app->session->getFlash('success') ?> <?php endif; ?>