Output ('',S); breaking code with Mpdf and PHPmailer - output

Question

I am trying to set up sending a pdf attachment with mPDF and PHPMailer.
mPDF is woking fine when output is download to browser, the minute I change it to Output('',S) the code stops working with Error 500 and I have tried different versions of the mailer code with no luck. I cant find any error with the syntax and all online tutorials seem to agree with the code. I am stumped
My code:
<?php
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;
require_once __DIR__ . '/vendor/autoload.php';
// Grab variables
$fname = $_POST['fname'];
$lname = $_POST['lname'];
$email = $_POST['email'];
$message = $_POST['message'];
$mpdf = new \Mpdf\Mpdf();
$data = "";
$data .= "<h1>Testing this</h1>";
//Add Data
$data .='<strong>First Name</strong> '. $fname.'<br>';
$data .='<strong>Last Name</strong> '. $lname.'<br>';
$data .='<strong>Email</strong> '. $email .'<br>';
if($message)
{
$data .='<br/><strong>Message</strong><br/> '. $message.'<br>';
}
//WritePdf
$mpdf->WriteHtml($data);
//output to bowser
$pdf = $mpdf->output('',S);
$enquirydata = [
'First Name' => $fname,
'Last Name' => $lname,
'Email' => $email,
'Message' => $message
];
sendEmail($pdf,$enquirydata);
function sendEmail($pdf, $enquirydata)
{
$mail = new PHPMailer(true);
try {
//Server settings
$mail->SMTPDebug = SMTP::DEBUG_SERVER; // Enable verbose debug output
$mail->isSMTP(); // Send using SMTP
$mail->Host = 'in-v3.mailjet.com'; // Set the SMTP server to send through
$mail->SMTPAuth = true; // Enable SMTP authentication
$mail->Username = 'username'; // SMTP username
$mail->Password = 'password'; // SMTP password
$mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS; // Enable TLS encryption; `PHPMailer::ENCRYPTION_SMTPS` encouraged
$mail->Port = 587; // TCP port to connect to, use 465 for `PHPMailer::ENCRYPTION_SMTPS` above
//Recipients
$mail->setFrom('myemails#gmail.com', 'Test Form');
$mail->addAddress('joe#example.net', 'Joe User'); // Add a recipient
$mail->addReplyTo('info#example.com', 'Information');
$mail->addCC('cc#example.com');
$mail->addBCC('bcc#example.com');
// Attachments
// Content
$mail->isHTML(true); // Set email format to HTML
$mail->Subject = 'Here is the subject';
$mail->Body = 'This is the HTML message body <b>in bold!</b>';
$mail->AltBody = 'This is the body in plain text for non-HTML mail clients';
$mail->send();
echo 'Message has been sent';
} catch (Exception $e) {
echo "Message could not be sent. Mailer Error: {$mail->ErrorInfo}";
}
}
?>

Answer 1

If you are in a localhost, comment the line with the validation $email->isSMTP();
It works for me in my local.