PHPMailer Not Working

<?php
// Import PHPMailer classes into the global namespace
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

// Include PHPMailer library files
require 'vendor/autoload.php';

// Create an instance of PHPMailer class
$mail = new PHPMailer(true);
// SMTP configuration
$mail->isSMTP();
$mail->Host     = 'smtp.mailgun.org';
$mail->SMTPAuth = true;
$mail->Username = '[email protected]';
$mail->Password = '1645e3da6b516b3220e6097d9432d850-73f745ed-8e219784';
$mail->SMTPSecure = 'tls';
$mail->Port     = 587;

// Sender info
$mail->setFrom('[email protected]', 'FromNate');


// Add a recipient
$mail->addAddress('[email protected]');


// Email subject
$mail->Subject = 'Send Email via SMTP using PHPMailer';

// Set email format to HTML
$mail->isHTML(true);

// Email body content
$mailContent = '
    <h2>Send HTML Email using SMTP Server in PHP</h2>
    <p>It is a test email by CodexWorld, sent via SMTP server with PHPMailer using PHP.</p>
    <p>Read the tutorial and download this script from <a href="https://www.codexworld.com/">CodexWorld</a>.</p>';
$mail->Body = $mailContent;

// Send email
if(!$mail->send()){
    echo 'Message could not be sent. Mailer Error: '.$mail->ErrorInfo;
}else{
    echo 'Message has been sent.';
}