Show Custom Post Types in Category Archive Page

By default WordPress custom post types do not appear in a category or tag archive page, to change this behaviour and display the custom post type you can add this filter/function to your themes functions.php file.

function themeprefix_show_cpt_archives( $query ) {
 if( is_category() || is_tag() && empty( $query->query_vars['suppress_filters'] ) ) {
 $query->set( 'post_type', array(
 'post', 'nav_menu_item', 'custom-post-type-name'
 return $query;
add_filter( 'pre_get_posts', 'themeprefix_show_cpt_archives' );

Just add your custom post type name to suit, or to add more than one just comma separate the names.

This uses the pre_get_posts filter – Ref