Undefined index: g-recaptcha-response

I am trying to implement Google's Official PHP ReCaptcha client with my attempt I am getting an error message:

Undefined index: g-recaptcha-response

My implementation as far as I can tell does pass the captcha response back to the form but I am not sure where i am making the mistake.

PHP:

<?php
//Show errors
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

//Load Required Components
require_once 'src/recaptcha_autoload.php';
require_once "functions.php";
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;
require 'src/Exception.php';
require 'src/PHPMailer.php';
require 'src/SMTP.php';

$errorsMSG = array(); // array to hold validation errors
$data = array(); // array to pass back data
// validate the variables ======================================================
// if any of these variables don't exist, add an error to our $errorsMSG array
if (empty($_POST['firstName'])) $errorsMSG['firstName'] = 'First Name is required.';
if (empty($_POST['lastName'])) $errorsMSG['lastName'] = 'Last Name is required.';
if (empty($_POST['companyName'])) $errorsMSG['companyName'] = 'Company Name is required.';
if (empty($_POST['companyAddress'])) $errorsMSG['companyAddress'] = 'Company Address is required.';
if (empty($_POST['city'])) $errorsMSG['city'] = 'City is required.';
// if (empty($_POST['state'])) $errorsMSG['state'] = 'State is required.';
if (empty($_POST['emailAddress'])) $errorsMSG['emailAddress'] = 'Email Address is required.';
if (empty($_POST['message'])) $errorsMSG['message'] = 'Message is required.';
// return a response ===========================================================
// if there are any errors in our errors array, return a success boolean of false
if (!empty($errorsMSG)) {
    // if there are items in our errors array, return those errors
    $data['success'] = false;
    $data['errorsMSG'] = $errorsMSG;
} else {
    checkRecaptcha();
}


function checkReCaptcha()
{
    // Declare Variables
    $gRecaptchaResponse = $_POST['g-recaptcha-response'];
    $remoteIp = get_client_ip();
    $secret = 'SECRET_KEY';

    // form submit check
    if (isset($_POST['submit']))
    {

        // Google reCAPTCHA response check
        if (isset($_POST['g-recaptcha-response']) && !empty($_POST['g-recaptcha-response']))
        {

            // Create an instance of the service using your secret
            $recaptcha = new \ReCaptcha\ReCaptcha($secret);
            $resp = $recaptcha->verify($_POST['g-recaptcha-response'], $_SERVER['REMOTE_ADDR']);
            // check if response is a success


            if ($resp->isSuccess())
            {

                //Send Email
                sendMail();
            }
            else
            {
                //Throw Error if Validation Failed
                $errMsg = 'Robot verification failed, please try again.';

            };

        }
        else
        {
            //Throw Error if User Forgot
            $errMsg = 'Please click on the reCAPTCHA box.';

        };

    }
    //End of Check Google Recaptcha Function

}


function sendMail() {
    $mail = new PHPMailer(true); // Passing `true` enables exceptions
    try {
        //Server settings
        $mail->SMTPDebug = 2; // Enable verbose debug output
        $mail->isSMTP(); // Set mailer to use SMTP
        $mail->Host = 'smtp.server.com'; // Specify main and backup SMTP servers
        $mail->SMTPAuth = true; // Enable SMTP authentication
        $mail->Username = 'user@server.com'; // SMTP username
        $mail->Password = 'SECRET_PASSWORD'; // SMTP password
        $mail->SMTPSecure = 'tls'; // Enable TLS encryption, `ssl` also accepted
        $mail->Port = 587; // TCP port to connect to
        //Recipients
        $mail->setFrom('user@server.com', 'Mailer');
        $mail->addAddress('user@server.com', 'Joe User'); // Add a recipient
        //Content
        $mail->isHTML(true); // Set email format to HTML
        $mail->Subject = 'New Message from Contact Form';
        //prepare email body
        $body_message = "";
        $body_message .= "Sender IP: " . get_client_ip() ."<br>";
        $body_message .= "First Name: " . $firstName ."<br>";
        $body_message .= "Last Name: " . $lastName ."<br>";
        $body_message .= "Company Name: " . $companyName ."<br>";
        $body_message .= "Company Address: " . $companyAddress ."<br>";
        $body_message .= "City: " . $city ."<br>";
        $body_message .= "State: " . $state ."<br>";
        $body_message .= "Sender email: " . $emailAddress ."<br>";
        $body_message .= "Sender Phone: " . $phoneNumber ."<br>";
        $body_message .= "\n\n". $message;

        $mail->Body = $body_message;
          $mail->send();
          $errorsMSG = 'Message successfully sent.';
        }
    catch(Exception $e) {
        $mail->ErrorInfo;
        $errorsMSG = 'There has been an issue sending your message.';
    }
    //End of sendMail Function
}

// return all our data to an AJAX call
echo json_encode($data);
?>

JS:

// Start
$(document).ready(function() {

    // process the form
    $('form').submit(function(event) {

        $('.form-group').removeClass('has-error'); // remove the error class
        $('.help-block').remove(); // remove the error text

        // get the form data
        // there are many ways to get this data using jQuery (you can use the class or id also)
        var formData = {
            'firstName'                 : $('input[name=firstName]').val(),
            'lastName'              : $('input[name=lastName]').val(),
            'companyName'               : $('input[name=companyName]').val(),
            'companyAddress'                : $('input[name=companyAddress]').val(),
            'city'              : $('input[name=city]').val(),
        //  'state'                 : $('input[name=state]').val(),
            'emailAddress'          : $('input[name=emailAddress]').val(),
            'message'   : $('input[name=message]').val(),
            'g-recaptcha'  : $("#g-recaptcha-response").val(),
        };

        // process the form
        $.ajax({
            type        : 'POST', // define the type of HTTP verb we want to use (POST for our form)
            url         : 'formMaster.php', // the url where we want to POST
            data        : formData, // our data object
            dataType    : 'json', // what type of data do we expect back from the server
            encode      : true
        })
            // using the done promise callback
            .done(function(data) {

                // log data to the console so we can see
                console.log(data);

                // here we will handle errorsMSG and validation messages
                if ( ! data.success) {

                    // handle errorsMSG for name ---------------
                    if (data.errorsMSG.firstName) {
                        $('#firstName-group').addClass('has-error'); // add the error class to show red input
                        $('#firstName-group').append('<div class="help-block">' + data.errorsMSG.firstName + '</div>'); // add the actual error message under our input
                    }

                    // handle errorsMSG for name ---------------
                    if (data.errorsMSG.lastName) {
                        $('#lastName-group').addClass('has-error'); // add the error class to show red input
                        $('#lastName-group').append('<div class="help-block">' + data.errorsMSG.lastName + '</div>'); // add the actual error message under our input
                    }

                    // handle errorsMSG for name ---------------
                    if (data.errorsMSG.companyName) {
                        $('#companyName-group').addClass('has-error'); // add the error class to show red input
                        $('#companyName-group').append('<div class="help-block">' + data.errorsMSG.companyName + '</div>'); // add the actual error message under our input
                    }

                    // handle errorsMSG for Company Address ---------------
                    if (data.errorsMSG.companyAddress) {
                        $('#companyAddress-group').addClass('has-error'); // add the error class to show red input
                        $('#companyAddress-group').append('<div class="help-block">' + data.errorsMSG.companyAddress + '</div>'); // add the actual error message under our input
                    }

                    // handle errorsMSG for Company Address ---------------
                    if (data.errorsMSG.city) {
                        $('#city-group').addClass('has-error'); // add the error class to show red input
                        $('#city-group').append('<div class="help-block">' + data.errorsMSG.city + '</div>'); // add the actual error message under our input
                    }

                    // handle errorsMSG for Company Address ---------------
            //      if (data.errorsMSG.state) {
            //          $('#state-group').addClass('has-error'); // add the error class to show red input
            //          $('#state-group').append('<div class="help-block">' + data.errorsMSG.state + '</div>'); // add the actual error message under our input
            //      }

                    // handle errorsMSG for Email Address ---------------
                    if (data.errorsMSG.emailAddress) {
                        $('#emailAddress-group').addClass('has-error'); // add the error class to show red input
                        $('#emailAddress-group').append('<div class="help-block">' + data.errorsMSG.emailAddress + '</div>'); // add the actual error message under our input
                    }

                    // handle errorsMSG for superhero alias ---------------
                    if (data.errorsMSG.message) {
                        $('#message-group').addClass('has-error'); // add the error class to show red input
                        $('#message-group').append('<div class="help-block">' + data.errorsMSG.message + '</div>'); // add the actual error message under our input
                    }

                } else {

                    // ALL GOOD! just show the success message!
                    $('form').append('<div class="alert alert-success">' + data.message + '</div>');

                    // usually after form submission, you'll want to redirect
                    // window.location = '/thank-you'; // redirect a user to another page

                }
            })

            // using the fail promise callback
            .fail(function(data) {

                // show any errorsMSG
                // best to remove for production
                console.log(data);
            });

        // stop the form from submitting the normal way and refreshing the page
        event.preventDefault();
    });

});

What am I missing or doing wrong? The files/resources are there and accessible.