200 response code calls the Ajax error callback

Question

The post method given below POSTs to a webhook which accepts 4 parameters - fields[message], fields[name], fields[email] and fields[url].

The webhook runs successfully. It initially sends the 200 response back to the client. Then it parses the parameters passed and executes as per requirement. I have also added response-message: "{}" to the response on the webhook.

The status code returned is 200 everytime. And yet, the error callback gets invoked in Ajax call.

// Static comments
(function ($) {
  var $comments = $('.js-comments');

  $('#comment-form').submit(function () {
    var form = this;

    $(form).addClass('disabled');
    $('#comment-form-submit').html('Loading...');

    $.ajax({
      type: $(this).attr('method'),
      url: $(this).attr('action'),
      data: $(this).serialize(),
      dataType: 'json',
      contentType: 'application/x-www-form-urlencoded',
      success: function (data) {
        $('#comment-form-submit').html('Submitted');
        $('#comment-form .js-notice').removeClass('notice--danger').addClass('notice--success');
        showAlert('<strong>Thanks for your comment!</strong> It will show on the site once it has been approved.');
      },
      error: function (err) {
        console.log(err);
        $('#comment-form-submit').html('Submit Comment');
        $('#comment-form .js-notice').removeClass('notice--success').addClass('notice--danger');
        showAlert('<strong>Sorry, there was an error with your submission.</strong> Please make sure all required fields have been completed and try again.');
        $(form).removeClass('disabled');
      }
    });

    return false;
  });

  function showAlert(message) {
    $('#comment-form .js-notice').removeClass('hidden');
    $('#comment-form .js-notice-text').html(message);
  }
})(jQuery);

This was giving me an Access-Control-Allow-Origin error, so I changed dataType: 'json', to dataType: 'jsonp',.

And now, the parameters being passed aren't getting parsed. And the error callback is still getting called. The webhook still returns a 200 status response code to the client.

The webhook runs from a YAML file, given below.

- id: "add-comment"
  execute-command: "./add-comment.sh"
  response-headers:
    - Access-Control-Allow-Origin: "*"
  response-message: "{}"
  pass-arguments-to-command:
    - source: payload
      name: fields[message]
    - source: payload
      name: fields[name]
    - source: payload
      name: fields[email]
    - source: payload
      name: fields[url]

I'm completely lost here. How do I get the success callback to be invoked? (status is 200, response body is {}, dataType is jsonp).