Validation tutorial

"I set up the rules WITHOUT any "required" rule, so it should pass if only one field is filled up.
In the debugbar the $_POST array ist correctly filled out, but the form everytime is still reloaded instead of showing my success-screen.

Where is my issue ?!?"

Try adding permit_empty to all rules. For ex: 'site_admin_name' => 'permit_empty|min_length[3]|max_lenght[250]',

Your guess has no effect