Facebook Webhook Url verification is returning with additional string on botman studio

Question

I am trying to verify my webhook url, however I am getting this error Here is my code:

$config = [

   'facebook' => [
          'token' => 'page-token',
                'app_secret' => 'app-secret',
                'verification' => env('VERIFY_TOKEN')
     ]

 ];

   DriverManager::loadDriver(FacebookDriver::class);
    
   $botman = BotManFactory::create($config);   


   $botman->listen();

As noticed aboved I am getting additonal string added on the hub_challenge request. How will I able to solved this problem?