Contact form plugin ajax submit URL not working

Question

I am using contact form plugin for forms in my craft website. For avoiding page redirection, I followed ajax submit for the form, but it is not redirected to controller code.

My form is as below:-

<form method="post" action="" accept-charset="UTF-8" class="basic-form" id="contactForm">
       {{ csrfInput() }}
       <input type="hidden" name="action" value="contact-form/send">
       <div class="form-group">
              <input type="text" class="text-field" id="text-630573652" name="firstName" value="" required="" placeholder="Name *" autocomplete="off">
       </div>
      <div class="layout-sm-12">
             <button type="submit" class="btn white-btn-outline submit-btn">LET'S TALK<i class="icon-long-arrow-bold-right"></i></button>
                    </div>
            </form>

My ajax script is as follows:-

$(function () {
        $('#contactForm').on('submit', function (e) {
        e.preventDefault();
        $.ajax({
            type: 'post',
            url: '/',
            data: $('#contactForm').serialize(),
            dataType: 'json',
            success: function (response) {
                 alert(response);
            }
        });

        });
});

For this I am getting error in console like 404 page not found. How to redirect to send controller index function using ajax request. As per other tutorials '/' is not working here.

Anyone please help...