Contact form doesn't work on Ubuntu VPS- DigitalOcean - error 405 Not Allowed nginx/1.4.6 (Ubuntu)

Question

I am hosting my website on VPN- DigitalOcean.

I installed NGinx, sendmail packages on ubuntu but I kept trying to

I kept having this problem whenever I try to send an email through contact form. The contact form uses php script

405 Not Allowed nginx/1.10.3 (Ubuntu)

What can i do? thanks in Advance. my website link is this: http://whitecodelabs.com/contact.html

<form id="contact-form" method="post" action="" role="form">
                <div class="messages"></div>
                <div class="controls">
                    <div class="form-group">
                        <!-- <label for="form_name">Firstname *</label> -->
                        <input id="form_name" type="text" name="form_name" class="form-control" placeholder="Name *" required="required" data-error="Name is required.">
                        <div class="help-block with-errors"></div>
                    </div>
                    <div class="form-group">
                        <!-- <label for="form_email">Email *</label> -->
                        <input id="form_email" type="email" name="form_email" class="form-control" placeholder="Email *" required="required" data-error="Valid email is required.">
                        <div class="help-block with-errors"></div>
                    </div>
                    <div class="form-group">
                        <!-- <label for="form_companyname">Company Name *</label> -->
                        <input id="form_companyname" type="text" name="form_companyname" class="form-control" placeholder="Company Name *" required="required" data-error="Company Name is required.">
                        <div class="help-block with-errors"></div>
                    </div>
                    <div class="form-group">
                        <!-- <label for="form_phone">Phone</label> -->
                        <input id="form_phone" type="tel" name="form_phone" class="form-control" placeholder="Phone *">
                        <div class="help-block with-errors"></div>
                    </div>
                    <div class="form-group">
                        <!-- <label for="form_message">Message *</label> -->
                        <textarea id="form_message" name="form_message" class="form-control" placeholder="Message *" rows="4" required data-error="Please,leave us a message."></textarea>
                        <div class="help-block with-errors"></div>
                    </div>
                    <div class="form-group">
                        <div class="recaptcha-wrapper">
                            <div class="g-recaptcha" data-sitekey="*************************"></div>
                        </div>
                    </div>
                    <button type="submit" class="submit_button" id="submit_request"> SUBMIT REQUEST</button>
                    <p class="text-muted"><strong>*</strong> These fields are required.</p>
                </div>

            </form>

jQuery Code is this used:

$(function () {

$('#contact-form').validator();

$('#contact-form').on('submit', function (e) {
    if (!e.isDefaultPrevented()) {
        var url = "/contact.php";
        $.ajax({
            type: "POST",
            url: url,
            data: $(this).serialize(),
            success: function (data)
            {
                console.log("SUCCESS", data);
                var messageAlert = 'alert-' + data.type;
                var messageText = data.message;

                var alertBox = '<div class="alert ' + messageAlert + ' alert-dismissable"><button type="button" class="close" data-dismiss="alert" aria-hidden="true">&times;</button>' + messageText + '</div>';
                if (messageAlert && messageText) {
                    $('#contact-form').find('.messages').html(alertBox);
                    $('#contact-form')[0].reset();
                }
            }
        });
        return false;
    }
  })
});

and contact.php code is this with captcha:

$from = 'hello@Email.com';
$sendTo = 'hello@Email.com';
$subject = 'New message from contact form';
$fields = array('form_name' => 'Name', 'form_companyname' => 'Company', 'form_phone' => 'Phone', 'form_email' => 'Email', 'form_message' => 'Message'); // array variable name => Text to appear in email
$okMessage = 'Thank you for reaching out. We will get back to you soon!';
$errorMessage = 'There was an error while submitting the form. Please try again later';

if(isset($_POST['g-recaptcha-response']) && !empty($_POST['g-recaptcha-response'])) {
//your site secret key
$secret = '**************************';
//get verify response data
$verifyResponse = file_get_contents('https://www.google.com/recaptcha/api/siteverify?secret='.$secret.'&response='.$_POST['g-recaptcha-response']);
$responseData = json_decode($verifyResponse);

        try
    {
        $emailText = "You have new message from contact form\n=============================\n";
        foreach ($_POST as $key => $value) {
            if (isset($fields[$key])) {
                $emailText .= "$fields[$key]: $value\n";
            }
        }

        mail($sendTo, $subject, $emailText, "From: " . $from);

        $responseArray = array('type' => 'success', 'message' => $okMessage);
    }
    catch (\Exception $e)
    {
        $responseArray = array('type' => 'danger', 'message' => $errorMessage);
    }

    if (!empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
        $encoded = json_encode($responseArray);

        header('Content-Type: application/json');

        echo $encoded;
    }
    else {
        echo $responseArray['message'];
    }
    } else {
      echo 'Please click on the reCAPTCHA box.';
    }