List all posts in taxonomy term

You should be using a tax_query for this operation. The category parameters won’t work with custom taxonomies

Instead of

'category' => $catID,

use

'tax_query' => array(
        array(
            'taxonomy'          => 'series',
            'field'             => 'term_id',
            'terms'             => $catID,
            'include_children'  => false
        ),
    ),