phpmailer not working, error log: Uncaught PHPMailer\PHPMailer\Exception: SMTP Error: Could not connect to SMTP host

Recently I built a website, Everything is working smooth but contact form is not sending email. I am doing it using a combination of jquery, php and PHPMailer php library. Please help me out. Here is the code:

php in a separate file named contact.php in a folder PHP:

<?php 
    require 'src/Exception.php';
    require 'src/PHPMailer.php';
    require 'src/SMTP.php';
    
    use PHPMailer\PHPMailer\PHPMailer;
    use PHPMailer\PHPMailer\Exception;
    use PHPMailer\PHPMailer\SMTP;

    $mail = new PHPMailer(true);
    $mail->IsSMTP();
    $mail->Mailer = "smtp";

    $mail->SMTPDebug = 3;
    $mail->isSMTP();
    $mail->Host       = 'smtp.gmail.com';
    $mail->SMTPAuth   = true;
    $mail->Username   = '<myemail>';                     
    $mail->Password   = '<secretpassword>';
    $mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;
    $mail->Port       = 587;


    $to = "<myemail>";
    $from = $_POST['email'];
    $first_name = $_POST['name'];

    $subject = "Contact form";
    $message = "Message: " . $_POST['textans'];
    $mail->SetFrom($from, $first_name);
    $mail->addAddress('<myemail>', 'Diode');
    $mail->Subject = $subject;
    $mail->Body=$message;
    $mail->send();
    
?>

According to the digging I have done the data is being passed to the PHP but is not being sent. I am using the website on AWS EC2. I checked telnet for connection, but telnet works so I am sure the host is reachable. I have also turned off the two-factor verification and turned on less secure apps.

I tried: 1) changing port to 465. 2) turning off autotls. 3) Checked that openssl is uncommented. 4) Checked inbound and outbound rules both in windows firewall and aws security

It give a post error (500 Internal server error) on the browser debugger. Here is the PHP log:

[<dateandtime> Asia/Kolkata] PHP Fatal error:  Uncaught PHPMailer\PHPMailer\Exception: SMTP Error: Could not connect to SMTP host. in <somelocation>\PHP\src\PHPMailer.php:2129
Stack trace:
#0 <somelocation>\PHP\src\PHPMailer.php(1953): PHPMailer\PHPMailer\PHPMailer->smtpConnect(Array)
#1 <somelocation>\PHP\src\PHPMailer.php(1635): PHPMailer\PHPMailer\PHPMailer->smtpSend('Date: Th...', ' Name: N...')
#2 <somelocation>\PHP\src\PHPMailer.php(1468): PHPMailer\PHPMailer\PHPMailer->postSend()
#3 <somelocation>\PHP\contact.php(37): PHPMailer\PHPMailer\PHPMailer->send()
#4 {main}
  thrown in <somelocation>\PHP\src\PHPMailer.php on line 2129

Also it works on localhost on XAMPP! Thanks for your help in advance.

Solution

First of all, I tried running your code which gave me SMTP Class not found error, so I added another use statement use PHPMailer\PHPMailer\SMTP; to avoid future errors.

Then, I got the same error and solved it by generating an App Password, which was required for 2-Step Verified accounts.

I didn't really change your code, but I ran it in localhost.

If nothing works, you can set the debug mode $mail->SMTPDebug = 3; in order to get more details, and also I recommend checking out the SSL/TLS protocols, which I saw it from this thread: PHPMailer: SMTP Error: Could not connect to SMTP host

I hope that I didn't waste your time...