The messages.send method in VkApi does not work. The bot does not send anything to the received message. How to decide?

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Hello. I'm trying to implement a VK chat bot, following the example from the documentation.
Here is my code -

<?php

require('../vendor/autoload.php');

$app = new Silex\Application();
$app['debug'] = true;

// Register the monolog logging service
$app->register(new Silex\Provider\MonologServiceProvider(), array(
  'monolog.logfile' => 'php://stderr',
));



// Our web handlers

$app->get('/', function() use($app) {
  return "Hi World";
});

$app->post('/bot', function() use($app) {
  
  
  $data = json_decode(file_get_contents('php://input'));
  
  if(!$data)
    return 'error1';
  
  if($data->secret !== getenv('VK_SECRET_TOKEN') && $data->type !== 'confirmation')
    return 'error1';
  
  switch($data->type) {
    case 'confirmation':
      return getenv('VK_CONFIRMATION_CODE');
      break;
    case 'message_new':
      $request_params = array(
        'user_id' => $data->object->from_id,
        'message' => 'Тест',
        'access_token' => getenv('VK_TOKEN'),
        'v' => '5.92'
      );
      file_get_contents('https://api.vk.com/method/messages.send?' . http_build_query($request_params));
      return 'ok';
      break;
  }
  
  return "error1";
});

$app->run();

All rights issued, the server connected. The bot itself is hosted on heroku.
For any word, the bot should send "Test". but nothing happens.

Answer 1

It's nice that I was invited as an expert, but I did not encounter such issues. I can advise you to turn on your head and debug:
1. Does the sending code work separately?
2. If the sending code works, are VK_TOKEN from the environment and $data->object->from_id sent correctly? Is it the same user ID (and in the right format)?
3. is it in $data->type -> 'message_new' ?
4. Does the request come to /bot?