I’ve been working on a website and added a form to make it send me an email but it keeps saying “404 not allowed”

<form action="emailhandler.php" method="post">
  Name:<br>
  <input type="text" name="name"><br>
  Email:<br>
  <input type="email" name="email"><br>
  Message:<br>
  <textarea name="message"></textarea><br><br>
  <input type="submit" value="Submit">
</form>

<?php
if($_SERVER["REQUEST_METHOD"] == "POST") {
  $name = $_POST['name'];
  $email = $_POST['email'];
  $message = $_POST['message'];
  $to = '-------------------(email hidden for privacy)';
  $subject = 'New message from your website';
  
  $headers = "From: " . $email;
  
  mail($to, $subject, $message, $headers);
  echo "Email sent!";
}
?>