Symfony 3 controller design for web application and json REST API - symfony

Question

I'm building a web application with Symfony 3 and I need a REST API for mobiles applications. I use FosUserBundle and FosRestBundle.
Here's a simple controller:
/**
* #Route("/titles/add", name="_addTitle");
* #param Request $request
* #return Response
*/
public function addAction(Request $request)
{
$title = new Title();
$title->setUserId($this->getUser()->getId());
$form = $this->createForm(NewTitle::class, $title);
$form->handleRequest($request);
if ($form->isSubmitted() && $form->isValid()) {
$this->get('title.manager')->saveTitle($title);
return $this->redirect('/contacts/add');
}
return $this->render('title/add.html.twig', array(
'form' => $form->createView()
));
}
/**
* #Post("/api/titles")
*/
public function postAction(Request $request)
{
$title = new Title();
$title->setUserId(1);
$form = $this->createForm(NewTitle::class, $title);
$form->submit($request->request->all());
if ($form->isValid()) {
$this->get('title.manager')->saveTitle($title);
return View::create($title, Codes::HTTP_CREATED);
}
return View::create($form, Codes::HTTP_BAD_REQUEST);
}
I have one action for the web application and one action for REST API. Business logic is in a "manager" service.
NewTitle Form Type :
class NewTitle extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('label', TextType::class)
->add('save', SubmitType::class, array('label' => 'Add title'));
}
public function configureOptions(OptionsResolver $resolver)
{
$resolver->setDefaults(array(
'csrf_protection' => false
));
}
}
My goal is to keep the code clean and avoid duplication. I have some questions :
Do you see a better way ?
in the postAction, when I have form errors it displays the "submit" field in my JSON response. How can I use same form class but "submit" element only for HTML form ?