php file not loading for html since adding reCAPTCHA v2

So, basically, I've made a website and the basic contact form php file worked fine. But as soon as I tried to add the recaptcha v2 stuff to control spam, it stopped working.

I keep getting errors whenever my html runs, and I'm not sure how to fix it.

I've looked up a bunch of different tutorials on the correct way to implement recaptcha v2, and theoretically, it should be fine. The only error I can see when I run the code, is that the PHP file no longer appears on the lefthand side of files being sourced by my browser.

Any help or advice out there?

Index.php Code:

<form name="contactForm" id="contactForm" action="php/contactForm.php" method="POST">
    <div class="control-group form-group">
        <div class="controls">
            <label>Full Name:</label>
            <input type="text" class="form-control" id="name" name="name" required="" data-validation-required-message="Please enter your name.">
            <p class="help-block"></p>
         </div>
     </div>
     <div class="control-group form-group">
         <div class="controls">
             <label>Phone Number:</label>
             <input type="tel" class="form-control" id="phone" name="phone">
         </div>
     </div>
     <div class="control-group form-group">
            <div class="controls">
                   <label>Email Address:</label>
                   <input type="email" class="form-control" id="email" name="email" required="" data-validation-required-message="Please enter your email address.">
            </div>
     </div>
     <div class="control-group form-group">
            <div class="controls">
                   <label>Subject:</label>
                   <input type="text" class="form-control" id="subject" name="subject" required="" data-validation-required-message="Please enter an email subject.">
                   <p class="help-block"></p>
            </div>
     </div>
     <div class="control-group form-group">
            <div class="controls">
                   <label>Message:</label>
                   <textarea rows="10" cols="100" class="form-control" id="message" name="message" required="" data-validation-required-message="Please enter your message" maxlength="999" style="resize:none"></textarea>
            </div>
     </div>
     <div class = "row">
            <div class = "col-md-6">
                   <div class="g-recaptcha" data-sitekey="MY_SITE_KEY" style = "text-align:left;"></div>
            </div>
            <div class = "col-md-6">
                   <div class = "submit" style = "text-align: right;">
                          <button id = "submitForm" type="submit" name = "submit" class="btn btn-primary btn-lg">Send Message</button>
                   </div>
            </div>
     </div>
</form>

contactForm.php:

<?php
if(isset($_POST['submit']))
{
    $secretKey = "MY_SECRET_KEY";
    $responseKey = $_POST['g-recaptcha-response'];
    $userIP = $_SERVER['REMOTE_ADDR'];

    $url = "https://www.google.com/recaptcha/api/siteverify?secret=$secretKey&response=$responseKey&remoteip=$userIP";

    $response = file_get_contents($url);

    $response = json_decode($response);

    if($response->success)
    {
        $email_to = "contact@emailaddress.com";
        $email_subject = "An Enquiry From Your Website";

        function died($error) {
            echo "We are very sorry, but there were error(s) found with the form you submitted. ";
            echo "These errors appear below.<br /><br />";
            echo $error."<br /><br />";
            echo "Please go back and fix these errors.<br /><br />";
            die();
        }

        if(!isset($_POST['name']) ||
            !isset($_POST['email']) ||
            !isset($_POST['phone']) ||
            !isset($_POST['subject']) ||
            !isset($_POST['message'])) {
            died('We are sorry, but there appears to be a problem with the form you submitted.');
        }

        $first_name = $_POST['name']; // required
        $email_from = $_POST['email']; // required
        $subject = $POST['subject']; // required
        $telephone = $_POST['phone']; // not required
        $comments = $_POST['message']; // required

        $error_message = "";
        $email_exp = '/^[A-Za-z0-9._%-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}$/';

        if(!preg_match($email_exp,$email_from)) {
        $error_message .= 'The Email Address you entered does not appear to be valid.<br />';
        }

        $string_exp = "/^[A-Za-z .'-]+$/";

        if(!preg_match($string_exp,$first_name)) {
        $error_message .= 'The Name you entered does not appear to be valid.<br />';
        }

        if(strlen($comments) < 2) {
        $error_message .= 'The Message you entered do not appear to be valid.<br />';
        }

        if(strlen($error_message) > 0) {
        died($error_message);
        }

        $email_message = "Form details below.\n\n";

        function clean_string($string) {
          $bad = array("content-type","bcc:","to:","cc:","href");
          return str_replace($bad,"",$string);
        }


        $email_message .= "Name: ".clean_string($first_name)."\n";
        $email_message .= "Email: ".clean_string($email_from)."\n";
        $email_message .= "Telephone: ".clean_string($telephone)."\n";
        $email_message .= "Subject: ".clean_string($subject)."\n";
        $email_message .= "Message: ".clean_string($comments)."\n";

        $headers = 'From: '.$email_from."\r\n".
        'Reply-To: '.$email_from."\r\n" .
        'X-Mailer: PHP/' . phpversion();
        $success = @mail($email_to, $email_subject, $email_message, $headers);

        if ($success)
        {
           echo "success";
        }
    }
    else
    {
        echo "Verification Fail";
    }
}
?>

Source files from browser DevTools on my webpage