How to redirect using a custom wordpress api endpoint after form submission?

I'm using a custom wordpress endpoint that I have defined in functions.php:

add_action('rest_api_init', function () {
    register_rest_route('custom_endpoint', 'submit-application', [
        'methods' => 'POST',
        'callback' => 'submit_application'
    ]);
});

I'm using the endpoint to process some form data sent via jetform builder. After the form data has been processed (various calls to an external api), I would like to redirect to a url that is returned by the api dynamically. Currently the business logic all succeeds, but I cannot for the life of me get the redirect to work. The form submits and displays a message "Form successfully submitted".

function submit_application ( $request ) {

  //Business logic here all succeeds

  $user= send_data($data);

  try {
      return new \WP_REST_Response(
          null, 
          303, 
          array(
              'Location' => $user['url'], 
          )
      );
      
  } catch (Exception $e) {
      return new WP_REST_Response( [
          'status' => 'error',
          'message' => $e->getMessage()
      ], 400 );
  }
}

I've also tried using

    wp_redirect( $user['url'] );
    exit();

The odd thing is I got it to work once, with what I think is this exact code, but suddenly after I continued development it stopped. It is also odd, because when I try the end point via postman instead of the form submission, it seems to receive the redirect correctly as well. Maybe that's indicative of a cache issue? I'm a little new to wordpress so any ideas would be very welcome!

Solution

In the end there were two things preventing me from redirecting the client directly from the custom Wordpress endpoint. Here is the redirect code that I included in the end of my endpoint

      return new \WP_REST_Response(
          null, 
          303, 
          array(
              'Location' => $user['portal_url'], 
          )
      );

The first issue was that JetForm was taking control of things and erroring out when the redirect was included for some reason. To fix this I just bypassed JetForm submission by targeting the form element and changing the action to go directly to my custom wordpress endpoint instead.

<script> 
    let form = document.querySelector('.jet-form-builder');
    form.action = "https://your-endpoint-url.com"
</script>

The last tidbit is that by doing this bypass I was receiving a nonce error so you either have to add some logic to account for this, or if you don't mind (i.e. you don't consider it a security vulnerability in your use case), just disable "Form Safety" in JetForm.