Validation form

Hello,

When trying to validate my form I think there is going something wrong, required fields shows messages on the first run. But when entering the Firstname and Passwords the Lastname doesn't validate anymore.

The code below is inside:  application/Config/Validation.php

PHP Code:

public $manager = [
    'Firstname'   => 'trim|required',
    'Lastname'    => 'trim|required',
    'Username'    => 'trim|required|valid_email',
    'Password'    => 'trim|required|min_length[8]',
    'Passconfirm' => 'trim|required|matches[Password]',
]; 


Is there something wrong, or is this a name conflict with the validation?