amp-form xhr submission

form-xhr.php

<?php
if (!empty($_POST)) {
  header("access-control-allow-credentials:true");
  header("access-control-allow-headers:Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token");
  header("access-control-allow-methods:POST, GET, OPTIONS");
  header("access-control-allow-origin:".$_SERVER['HTTP_ORIGIN']);
  header("access-control-expose-headers:AMP-Access-Control-Allow-Source-Origin");
  
  // I changed the protocol to HTTP since I was testing the site locally using BrowserSync, http://localhost:3000
  
  header("amp-access-control-allow-source-origin:http://".$_SERVER['HTTP_HOST']);
  header("Content-Type: application/json");
  $email = isset($_POST['email']) ? $_POST['email'] : '';
  $output = ['email' => $email];
  header("Content-Type: application/json");
  echo json_encode($output);
  $post_data['email'] = urlencode($_POST['email']);
  foreach($post_data as $key => $value) {
    $post_items[] = $key.
      '='.$value;
  }
  $post_string = implode('&', $post_items);
  $curl_connection = curl_init('http://formspree.io/myemailhere');
  curl_setopt($curl_connection, CURLOPT_CONNECTTIMEOUT, 30);
  curl_setopt($curl_connection, CURLOPT_RETURNTRANSFER, true);
  curl_setopt($curl_connection, CURLOPT_SSL_VERIFYPEER, false);
  curl_setopt($curl_connection, CURLOPT_FOLLOWLOCATION, 1);
  curl_setopt($curl_connection, CURLOPT_POSTFIELDS, $post_string);
  curl_exec($curl_connection);
  curl_close($curl_connection);
}
?>