Module \Helper\Acceptance could not be found and loaded

I am new to Codeception. I followed the instructions on the Quick start page (https://codeception.com/quickstart) and saw the error "Module \Helper\Acceptance could not be found and loaded" on step 6.

My folder structure is

 -tests
   -_output
   -acceptance
   -functional
   -Support
     -_generated
     -Data
     -Helper
       -Acceptance.php

   -unit
   -acceptance.suite.yml
   -functional.suite.yml
   -unit.suite.yml 

  -vendor
  -codeception.yml
  -composer.json
  -composer.lock

The /Helper/Acceptance.php:

<?php
namespace Helper;



class Acceptance extends \Codeception\Module
{


}

acceptance.suite.yml:

actor: AcceptanceTester
modules:
    enabled:
        - PhpBrowser:
            url: http://localhost/myapp
        - \Helper\Acceptance
step_decorators: ~

Any suggestions? Thank you in advance.