Template for custom post type when taxonomy is in the URL

Question

I have custom post type called books. This has a category taxonomy, called book_types. So, for example:

Books -> Fiction -> Da Vinci Code

• Custom Post Type: Books
• Custom Taxonomy: Book Types (fiction, non fiction, etc)
• Single entry: Da Vinci Code

I have the permalinks structure to be:

/books/fiction#da-vinci-code 

All the books are listed in their taxonomy category page as shown above. Da Vinci Code is just one part of the page for Fiction... as seen from the #da-vinci-code hashed value in the URL.

This means the taxonomy template is the important one. So I have a template:

template-book_types.php 

But this doesn't work. WP gives a 404. What am I missing? My code to create the CPT and Taxonomy is below. (And yes, I have flushed the Permalinks many times.)

/**
 * Post Type: Books.
 */

$labels = [
    "name" => __( "Books", "custom-post-type-ui" ),
    "singular_name" => __( "Book", "custom-post-type-ui" ),
];

$args = [
    "label" => __( "Books", "custom-post-type-ui" ),
    "labels" => $labels,
    "public" => true,
    "publicly_queryable" => true,
    "show_ui" => true,
    "show_in_rest" => true,
    "rest_base" => "",
    "rest_controller_class" => "WP_REST_Posts_Controller",
    "has_archive" => true,
    "show_in_menu" => true,
    "show_in_nav_menus" => true,
    "delete_with_user" => false,
    "exclude_from_search" => false,
    "capability_type" => "post",
    "map_meta_cap" => true,
    "hierarchical" => false,
    "can_export" => true,
    "rewrite" => [ "slug" => "books", "with_front" => true ],
    "query_var" => true,
    "menu_position" => 5,
    "menu_icon" => "dashicons-schedule",
    "supports" => [ "title", "editor" ],
    "taxonomies" => [ "book_types" ],
    "show_in_graphql" => false,
];

register_post_type( "books", $args );






/**
 * Taxonomy: Book Types.
 */

$labels = [
    "name" => __( "Book Types", "custom-post-type-ui" ),
    "singular_name" => __( "Book Type", "custom-post-type-ui" ),
];


$args = [
    "label" => __( "Book Types", "custom-post-type-ui" ),
    "labels" => $labels,
    "public" => true,
    "publicly_queryable" => true,
    "hierarchical" => true,
    "show_ui" => true,
    "show_in_menu" => true,
    "show_in_nav_menus" => true,
    "query_var" => true,
    "rewrite" => [ 'slug' => 'book_types', 'with_front' => true, ],
    "show_admin_column" => true,
    "show_in_rest" => true,
    "show_tagcloud" => false,
    "rest_base" => "book_types",
    "rest_controller_class" => "WP_REST_Terms_Controller",
    "show_in_quick_edit" => false,
    "sort" => false,
    "show_in_graphql" => false,
];
register_taxonomy( "book_types", [ "books" ], $args );

Answer 1

Your taxonomy's rewrite base is actually book_types (see the "rewrite" => [ 'slug' => 'book_types', 'with_front' => true, ] in your code), so the taxonomy archive pages are accessible at the /book_types/<term slug> path.. and not /books/<term slug>. So it's normal if /books/fiction shows a 404 error page, unless of course if there's a post with the slug fiction.

Secondly, note that 'with_front' => true means if your Custom Structure setting on the Permalink Settings admin page uses a prefix like /blog/ (with or without the leading/first slash), then your taxonomy's terms would also have that prefix in the permalink, e.g. https://example.com/blog/book_types/fiction/.

And the same also applies to post types where the with_front is set to true. So for example, https://example.com/blog/books/da-vinci-code/ would be the permalink for the "Da Vinci Code" post.

So as for the 404 error in question, try loading /book_types/fiction#da-vinci-code instead and check if you're seeing the correct taxonomy archive.

Also, you should know that the template name for a taxonomy archive should actually be in this form: taxonomy-<taxonomy>.php — or taxonomy-<taxonomy>-<term>.php for a specific term in a taxonomy, so you should rename your template from template-book_types.php to taxonomy-book_types.php so that WordPress loads it correctly on the taxonomy archive.

See https://developer.wordpress.org/themes/template-files-section/taxonomy-templates/ for more details.