How can I make this custom menu work?

You need to target the appropriate theme_location.

Assuming you’ve defined multiple nav menu locations using register_nav_menus() in functions.php:

<?php
register_nav_menus( array(
    'primary-menu' => 'Primary Menu',
    'secondary-menu' => 'Secondary Menu'
) );
?>

Then you call wp_nav_menu() using the appropriate theme_location as defined above, along with any other relevant arguments, e.g.:

<?php
wp_nav_menu( array(
    'theme_location' => 'primary-menu',
    'menu_class' => 'topnav'
) );

wp_nav_menu( array(
    'theme_location' => 'secondary-menu',
    'menu_class' => 'subnav'
) );
?>

Also, note that some of your arguments, such as menu_order, are not valid arguments for wp_nav_menu(). Here are the defaults:

<?php $defaults = array(
  'theme_location'  => ,
  'menu'            => , 
  'container'       => 'div', 
  'container_class' => 'menu-{menu slug}-container', 
  'container_id'    => ,
  'menu_class'      => 'menu', 
  'menu_id'         => ,
  'echo'            => true,
  'fallback_cb'     => 'wp_page_menu',
  'before'          => ,
  'after'           => ,
  'link_before'     => ,
  'link_after'      => ,
  'items_wrap'      => '<ul id=\"%1$s\" class=\"%2$s\">%3$s</ul>',
  'depth'           => 0,
  'walker'          => );
?>

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