Trying to implement a phpmailer into my project - php

Question

I am new to php but I would like to use a phpmailer in my project. I have followed the steps from here: https://github.com/PHPMailer/PHPMailer but the form somehow does not send and I get a 404 problem. Can anyone help me understand what it is that I am doing wrong here?
My html file:
<div class="container">
<form method="POST" action="form.php">
<div class="section7">
<div>
<input type="text" name="company" placeholder="Firma*" required><br>
<input type="text" name="surname" placeholder="Nazwisko*" required><br>
<input type="email" name="email" placeholder="E-mail*" required><br>
<textarea name="message" placeholder="Wiadomość*" required></textarea>
</div>
<div>
<input type="text" name="address_code" placeholder="Kod pocztowy*" required><br>
<input type="text" name="name" placeholder="Imię*" required><br>
<input type="tel" name="phone" placeholder="Nr telefonu*" required>
</div>
</div>
<div class="checkbox">
<label for="policy"></label><input type="checkbox" id="policy" name="policy" value="policy" required>
</label>Wyrażam zgodę na przetwarzanie moich danych osobowych zgodnie z ustawą z dnia 29.08.1997 (Dz.U.nr 133,poz.883) o ich ochronie.</label><br>
</div>
<div class="btn-submit">
<input type="submit" value="Wyślij">
</div>
</form>
</div>
My php form file:
<?php
require_once('mailer/class.phpmailer.php');
require_once('mailer/class.smtp.php');
require_once('mailer/PHPMailerAutoload.php');
require_once('phpmaileroauthgoogle.php');
header('Content-Type: application/json');
$mail = new PHPMailer(true);
try {
$name = $_POST['name'];
$surname = $_POST['surname'];
$company = $_POST['company'];
$email = $_POST['email'];
$tel = $_POST['phone'];
$address = $_POST['address_code'];
$messageText = $_POST['message'];
if (empty($name) || empty($email) || empty($tel) || empty($messageText) || empty($surname) || empty($company) || empty($address)) {
http_response_code(400);
echo json_encode("All fields are required.");
exit;
}
$messageText .= "\nNumer telefonu: " . $tel;
$mail->isSMTP();
$mail->CharSet = "UTF-8";
$mail->FromName = "$name";
$mail->Host = "smtp.gmail.com";
$mail->Mailer = "smtp";
$mail->SMTPAuth = true;
$mail->Port = 465;
$mail->SMTPSecure = "ssl";
$mail->SMTPAutoTLS = false;
$mail->Username = "myemail";
$mail->Password = "mypassword";
$mail->SetFrom("myemail");
$mail->Subject = "Message sent from xxx website";
$mail->Body = $messageText;
$mail->AddAddress("myemail");
$mail->AddReplyTo($email);
if ($mail->send()) {
echo json_encode("Thank you the message has been sent.");
} else {
http_response_code(400);
echo json_encode("Sorry, there was an error");
}
} catch (\Exception $e) {
echo "Message could not be sent. Mailer Error: {$mail->ErrorInfo}";
}
?>