Codeigniter website PHP code theme not working to register & Login

The problem seems to be with $password, it has no value.Try this way:

Code:

    function _check_login()
    {
        // limit number of login attempts
        $ok_to_login = $this->users_model->login_attempts();

        if ($ok_to_login)
        {
            $login = $this->users_model->login($this->input->post('username', TRUE), $this->input->post('password',TRUE));

            if ($login)
            {
                //your site secret key
                $secret = $this->settings->google_secret;

By some chance i fixed the problem in logging in now it works on http://netpay.epizy.com/ my website but i see a new problem that when i click the Admin dashboard it redirects to
This page isn’t working netpay.epizy.com is currently unable to handle this request.
HTTP ERROR 500
What to do to fix this ?