Nav menu from plugin to theme

wp_nav_menu() doesn’t accept a single value for a parameter, it takes an array. Proper format (if you are looking to simply call the menu by ID) would look like this:

wp_nav_menu(
    array(
        'menu' => $menu_id
    )
);

I’d recommend checking out the full reference in the codex for more information on the available parameters for displaying a menu.