code: public function actionSignUp() {
  
  		// Create Form Model
  		$model = new SignUpForm();
  
  		// Load and Validate Form Model
  		if( $model->load( Yii::$app->request->post(), 'Newsletter' ) && $model->validate() ) {
  
  			if( $this->newsletterMemberService->signUp( $model ) ) {
  
  				// Trigger Ajax Success
  				return AjaxUtil::generateSuccess( Yii::$app->newsletterMessage->getMessage( NewsletterGlobal::MESSAGE_NEWSLETTER_SIGNUP ) );
  			}
  		}
  
  		// Generate Errors
  		$errors = AjaxUtil::generateErrorMessage( $model );
  
  		// Trigger Ajax Failure
  		return AjaxUtil::generateFailure( Yii::$app->coreMessage->getMessage( CoreGlobal::ERROR_REQUEST ), $errors );
  	}
docs: SiteController ------------------------