Codeigniter 4 form validation example, please.

Hello.
I'm loosing my head now with something I cannot achieve.

Imagine a view with a simple form.
A controller with 2 methods: one to echo the view. The other to process the form after submission.

Controller (home):

PHP Code:

public function index(){        
    return view('form');
}

public function submission(){
    $result = $this->validate([
        'username' => 'required',
        'password' => 'required'
    ]);

    if(!$result){
        return redirect()->back()->withInput();
    } else {
        echo 'Submission OK!';
    }
} 


View (form)

PHP Code:

<?= $this->validator->listErrors() ?>


    <?= form_open('home/submission')?>

    <div>        
        <input type="text" name="username" value="<?= old('username') ?>">
    </div>
    <div>        
        <input type="text" name="password" value="<?= old('password') ?>">
    </div>
    <div>
        <input type="submit" value="Login">
    </div>
    </form> 


Question: How can I redirect to back, with input data AND with the validation errors so I can display them in the form view?