<?php header("Access-Control-Allow-Origin:*"); // Allow all origins

$InputAction = $_POST["Action"]; // Eventhandler

if ($InputAction == "Register") {
      echo("-400") } ?>

XMLHttpRequest cannot load http://api.proxy.wtf/debug.php. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://192.168.0.14:50001' is therefore not allowed access. The response had HTTP status code 500.

<?php
header("Access-Control-Allow-Origin:*"); // Allow all origins

require('includes/config.php'); // Prerequisite

/** Numeric callbacks (!negative values!)
-200 Registration successful; validation mail sended
-250 Username OK

-300 Username too short
-301 Username already in use
-302 Password too short
-303 Invalid email address
-304 Email already in use
-305 Error while registration

-400 Illegal request
**/

$InputAction = $_POST["Action"]; // Eventhandler

$InputUsername = $_POST["Username"]; // Requesting username
$InputMailaddress = $_POST["Mailaddress"]; // Requesting mail address
$InputPassword = $_POST["Password"]; // Requesting password

if ($InputAction == "Register") { // Action: Register
   if(strlen($InputUsername) < 3){ // Check Username length
      $error[] = 'Username is too short.';
      echo("-300");
   } else { // Check if username already exists
      $stmt = $db->prepare('SELECT username FROM members WHERE username = :username');
      $stmt->execute(array(':username' => $InputUsername));
      $row = $stmt->fetch(PDO::FETCH_ASSOC);
      echo("-250");

      if(!empty($row['username'])){ // If username already taken
         $error[] = 'Username provided is already in use.';
         echo("-301");
      }
   }
}
else {
   echo("-400");
}
?>