Unable to use validation rules that I set to the Config file

Hi, I am trying to perform form validation for user registration page with CodeIgniter 4. To do this I have written below codes in Validation.php file located in Config directory.

Config/Validation.php

PHP Code:

    public $userSignUp = [
        'username' => [
            'rules' => 'required|min_length[3]|max_length[50]',
            'errors' => [
                'required'    => 'You must choose a username.',
                'min_length'  => 'Username must have at least 3 characters',
                'max_length'  => 'Username can not have more than 50 characters'
            ]
        ],
        'email' => [
            'rules' => 'required|max_length[100]|valid_email|is_unique[user.email]',
            'errors' => [
                'required'    => 'You must enter email address',
                'max_length'  => 'Email address can not have more than 100 characters',
                'is_unique'   => 'The email address must be unique',
                'valid_email' => 'Please check the Email field. It does not appear to be valid.'
            ]
        ],
        'password' => [
            'rules' => 'required|min_length[8]|max_length[255]',
            'errors' => [
                'required'    => 'You must enter a password.',
                'min_length'  => 'Password must have at least 8 characters',
                'max_length'  => 'Password can not have more than 255 characters'
            ]
        ]
    ]; 


Then I get this "userSignup" rule in my Users controller.

Controllers/Users.php

PHP Code:

<?php namespace App\Controllers;
class Users extends BaseController
{
    public function __construct(){
            
        helper(['url', 'form']);         
    }
     
    public function index()
    {
        if($this->request->getMethod() == 'post') {

            $validation = \Config\Services::validation(); 
            $rules= $validation->getRuleGroup('userSignup');

            if(!$this->validate($rules)) {
                $data['validation'] = $this->validator;
                return view('user_register', $data);
            }
            
        } else {
            return view('user_register');
        }
    }


} 


Finally, to display those errors in the registration page.

Views/user_register.php

PHP Code:

<?php if(isset($validation)): ?>
       <div class="col-12">
            <div class="alert alert-danger alert-dismissible fade show" role="alert">
                 <?php echo $validation->listErrors() ?>
                 <button type="button" class="close" data-dismiss="alert" aria-label="Close">
                      <span aria-hidden="true">&times;</span>
                 </button>
             </div>
        </div>
 <?php endif; ?>

But, when I submit the form, I get this error "userSignup is not a validation rules group". What is going wrong with my code?