functions.php

function notify_post ($post_id) {
  $request = new WP_REST_Request('GET', '/wp/v2/posts/' . $post_id);
  $response = rest_do_request($request);
  $status = $response->get_status();
  $data = $response->get_data();
  $callback_uri = 'https://example.com';
  wp_safe_remote_post($callback_uri, array('body' => json_encode($data)));
}
add_action('post_updated', 'notify_post');