Custom WP Login /w redirection and error fields

custom-wp-login.php

<?php
function custom_login_shortcode() {
    if ( ! is_user_logged_in() ) { // Display WordPress login form:
        $args = array(
            'redirect' => home_url() . '/alumni/', 
            'form_id' => 'loginform-custom',
            'label_username' => __( 'Korisničko ime ili Email' ),
            'label_password' => __( 'Lozinka' ),
            'label_remember' => __( 'Zapamti me' ),
            'label_log_in' => __( 'Prijavi se' ),
            'remember' => true
        );
        wp_login_form( $args );
        echo '<a href="' . wp_lostpassword_url( get_permalink() ) . '">' . __( "Izgubili ste lozinku?" ) . '</a>';
        $login  = (isset($_GET['login']) ) ? $_GET['login'] : 0;
        if ( $login === "failed" ) {
          echo '<p class="login-msg"><strong>ERROR:</strong> Invalid username and/or password.</p>';
        } elseif ( $login === "empty" ) {
          echo '<p class="login-msg"><strong>ERROR:</strong> Username and/or Password is empty.</p>';
        } elseif ( $login === "false" ) {
          echo '<p class="login-msg"><strong>ERROR:</strong> You are logged out.</p>';
        }
        echo '<div class="login-wrap" style="margin-top: 50px;">';
        echo "<h4><strong>Nemate profil?</strong></h4>";
        echo "<h5>Postanite deo Alumni kluba</h5></br>";
        echo '<a class="btn-full btn-border"> KREIRAJ NALOG </a>';
        echo "</div>";
        

    } else { // If logged in:
        wp_loginout( home_url() . '/alumni/' ); // Display "Log Out" link.
        echo " | ";
        wp_register('', ''); // Display "Site Admin" link.
    }
}
add_shortcode( 'custom-login', 'custom_login_shortcode' );

function login_failed() {
  $login_page  = home_url( 'alumni/pridruzite-se/prijavi-se/' );
  wp_redirect( $login_page . '?login=failed' );
  exit;
}
// add_action( 'wp_login_failed', 'login_failed' );
 
function verify_username_password( $user, $username, $password ) {
  $login_page  = home_url( 'alumni/pridruzite-se/prijavi-se/' );
    if( $username == "" || $password == "" ) {
        wp_redirect( $login_page . "?login=empty" );
        exit;
    }
}
// add_filter( 'authenticate', 'verify_username_password', 1, 3);