Validation doesn't work

When the field is empty (invalid), you redirect to "/comic/create".
That is the browser send another request to the server.
So the $validation in the view is not the same instance as the Validation instance in the first request.

You saved the Validation instance into the flash message in the session.
You need to get it from the session.

See https://codeigniter4.github.io/CodeIgnit...ion-errors

Thank you! This one is work for me as well, I don't know if it's the good or the perfect one but at least, I've tried to find the code by myself and proud of myself because I can figure it out. 

PHP Code:

<?= session()->getFlashdata('validation') ? 'is-invalid' : '';  ?>