How create an event Calendar outlook PHP - php

Question

I find the second part (from header to the end) code in a site: it only download a file ics but it doesn't add in my calendar. However the 1st part is about sending mail and it's working !
<?php
$mailSub = "Invitation";
$mailMsg = "Bonjour";
require '../PHPMailer-master/PHPMailerAutoload.php';
$mail = new PHPMailer();
$mail->IsSmtp();
$mail->SMTPDebug = 2;
$mail->SMTPAuth = true;
$mail->SMTPSecure = 'tls';
$mail->Host = "smtp.live.com";
$mail->Port = 587; // or 587
$mail->IsHTML(true);
$mail->Username = "**************";
$mail->Password = "*****************";
$mail->setFrom('*****************');
$mail->Subject = $mailSub;
$mail->Body = $mailMsg;
$mail->AddAddress($mailto);
//$mail->Send();
if(!$mail->send()){
echo "Mailer Error: " . $mail->ErrorInfo;
}else{
echo "E-Mail has been sent";
}
header("Content-Type: text/Calendar");
header("Content-Disposition: inline; filename=calendar.ics");
echo "BEGIN:VCALENDAR\n";
echo "VERSION:2.0\n";
echo "PRODID:-//Foobar Corporation//NONSGML Foobar//EN\n";
echo "METHOD:REQUEST\n"; // requied by Outlook
echo "BEGIN:VEVENT\n";
echo "UID:".date('Ymd').'T'.date('His')."-".rand()."-example.com\n"; //required by Outlok
echo "DTSTAMP:".date('Ymd').'T'.date('His')."\n"; // required by Outlook
echo "DTSTART:20180909T000000\n";
echo "SUMMARY:TEST\n";
echo "DESCRIPTION: this is just a test\n";
echo "END:VEVENT\n";
echo "END:VCALENDAR\n";
?>