I cannot send an email from the form on my web to my gmail account with PHP Mailer

As the reference on the subject, I have been struggling to make a system which I can get an email from the form on the website. I use a server, HostGator. What I did is below

1. Created the form on the contact page embraced form tags, having method="POST" action="send.php".
2. Created my mail account on HostGator

3. I filled all the information about the host on send.php which shows a PHP Mailer basic format.

   4.After cricking the button named, "submit", the error shows like "This page isn't working. localhost is currently unable to handle this request. HTTP ERROR 500". Thus, I have been stack here now.

The name of my project folder is "businessWeb". The directory of all the folders inside it is below

•businessweb/vender/composer/...
•businesswebvender/phpmailer/...

<?php
// Import PHPMailer classes into the global namespace
// These must be at the top of your script, not inside a function
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

//Load composer's autoloader
require './vendor/autoload.php';

// get variables from the form
$name = filter_var($_POST['name'],FILTER_SANITIZE_STRING);
$phone = filter_var($_POST['phone'],FILTER_SANITIZE_STRING);
$email = filter_var($_POST['email'],FILTER_SANITIZE_STRING);
$message = filter_var($_POST['message'],FILTER_SANITIZE_STRING);

$mail = new PHPMailer(true);                              // Passing `true` enables exceptions
try {
    //Server settings
    $mail->SMTPDebug = 0;                                 // Enable verbose debug output
    $mail->isSMTP();                                      // Set mailer to use SMTP
    $mail->Host ='the address in Incoming section on Cpanel in HostGator ';  // Specify main and backup SMTP servers
    $mail->SMTPAuth = true;                               // Enable SMTP authentication
    $mail->Username = 'email on hostGator';                 // SMTP username
    $mail->Password = '***';                           // SMTP password
    $mail->SMTPSecure = 'ssl';                            // Enable TLS encryption, `ssl` also accepted
    $mail->Port = 465;                                    // TCP port to connect to

    //Sender
    $mail->setFrom('email on HostGator', 'Joey Namiki');
    //Recipients
    $mail->addAddress('my gmail account', 'Joey');     
    //Body Content
    $body = "<p>Hello<br /><br /> You have received an enquiry from<br /> " . $name . "<br /><br /> The message is <br />" . $message . "<br /><br />You can contact on <br /> " . $phone . "</p>";

    //Content
    $mail->isHTML(true);                                  // Set email format to HTML
    $mail->Subject = 'JoeyNamiki Website Enquiry from '. $name;
    $mail->Body    = $body;
    $mail->AltBody = strip_tags($body);

    $mail->send();

    header('location: thankyou.php');

} catch (Exception $e) {
    echo 'Message could not be sent.';
    echo 'Mailer Error: ' . $mail->ErrorInfo;
}
?>