Get JSON response from server using form with iFrame, PHP

I have a form that contains file upload inputs, I use iframe to submit those files and the rest data via ajax:

<form id="myform" action="/megogo/web/index.php?r=form/create-order" method="post" enctype="multipart/form-data" target="upload_target">
            ..inputs, file inputs..
</form>
<iframe id="upload_target" name="upload_target" src="#"></iframe> 

I receive data correctly on the server, but I cannot send response status back to the client:

public function actionCreateOrder(){
    //gettting data from $_POST
     $status = 1;
    \Yii::$app->response->format = Response::FORMAT_JSON;
    return $status;
}

Now when form is submitted I receive:

$("#myform").submit( function(e){    

      $.ajax({               
            success: function (response) 
            {    
               console.log(response);
            }
        });

  });

I get html page for response and the message Resource interpreted as Document but transferred with MIME type application/json:. How can I access my status instead? I cannot change enctype because I will not receive uploaded files then. Id appreciate any advice.