You forgot to add action hook on your code. Please use below the action
add_action( 'init', 'create_book_taxonomies', 0 );
Related Posts:
- Using wp_query is it possible to orderby taxonomy?
- “tax_query” parameter not working with WP_Query
- How do I exclude a custom taxonomy from the post loop
- get_posts assigned to a specific custom taxonomy term, and not the term’s children
- How can I get only parent terms?
- How to modify a taxonomy that’s already registered
- Retrieve posts by term id custom query
- Change order of Custom Taxonomy List
- Get the the top-level parent of a custom taxonomy term
- get_the_term_list without links in 3.1
- Inserting terms in an Hierarchical Taxonomy
- get_terms – only top level
- Custom taxonomy terms not showing as list Gutenberg Editor
- Altering the appearance of custom taxonomy inputs
- How to only list the child terms of a taxonomy and not their parents?
- Get term SLUG by term ID
- Is ACF being a honey trap? [closed]
- Get term name from term ID?
- Check if Current Category has Children
- How to use taxonomies on attachments with the new Media Library?
- Hierarchical taxonomy UI
- WordPress taxonomy radio buttons
- How to prevent new terms being added to a custom taxonomy?
- Custom taxonomy, get_the_terms, listing in order of parent > child
- How to remove the tag cloud from custom taxonomy admin page?
- custom taxonomy and pages rewrite slug conflict gives 404
- Inserting a term into a custom taxonomy
- Count posts in custom taxonomy
- How to add images to taxonomies?
- Read-only taxonomy (user can assign term but can’t create or edit existing terms)
- Remove taxonomy base or term from url
- Can you add the visual editor to the description field for custom taxonomies?
- Adding Category/Tag/Taxonomy Support to Images/Media
- Add default WordPress tag meta box to User Profile
- Custom Taxonomy Endpoint Pagination using paginate_links()
- How do I get the top-level terms in a custom taxonomy?
- Check if a post has any term in this custom taxonomy?
- Query Custom Post by Taxonomy Category
- Custom columns on edit-tags.php main page
- Loop through custom taxonomies and display posts
- How do I add a custom taxonomy as an option for menus under “Appearance” > “Menus”
- custom post type taxonomy “tag” archive : no post found
- How to get WooCommerce Product Category Link by ID?
- Order get_terms using a Custom Field
- Add custom taxonomy fields when creating a new taxonomy
- get_term_children for immediate children only (not grandchildren)
- Using pre_get_posts to rewrite search query to display posts from multiple taxonomies
- Custom taxonomies capabilities
- Contact Form 7 – Populate Select List With Taxonomy [closed]
- Can’t get a custom template taxonomy page to display
- Query users by custom taxonomy and user role
- Display category posts grouped by taxonomy
- WP REST API no longer supports filter param, so how do I get posts in a custom taxonomy?
- Custom Taxonomy and Tax_Query
- Custom Taxonomy Archive Page
- How to display custom taxonomies in posts?
- Get taxonomy names by post id
- Include and Exclude Taxonomies From Archives & Feeds Using ‘pre_get_posts’
- How to assign multiple roles for capabilities array withini register_taxonomy function?
- Filtering custom taxonomies
- Can custom taxonomies be displayed inside of a custom meta box?
- Determine Term depth
- Exclude Specific Term from Search
- How to get current term in my custom taxonomy in WordPress?
- WordPress database error: [Not unique table/alias: ‘wp_postmeta’]
- Is there a way to ‘Lock’ a Taxonomy?
- Bulk term assignment for attachment taxonomies
- Creating Custom Taxonomy without mapping to any post type
- Using WordPress to make a “Product Search” type navigation drilldown
- Hide the term description on the term edit page, for a given taxonomy
- Why is my working Custom Taxonomy not in get_taxonomies array?
- Add post classes for custom taxonomies to custom post type?
- Custom taxonomy listing page when no term set (all terms)
- get_terms does not return any results for my custom taxonomy?
- Order terms by term_order
- get_term_by not working when in functions.php
- How to modify the query in taxonomy-custom.php to sort term archives by a custom meta field?
- Custom taxonomy hide meta box but show in menu
- Creating a non-removable taxonomy term
- How To Change Custom Taxonomy To Radio Buttons
- Adding An Image To A Custom Taxonomy Term
- Custom Taxonomy not working with posts_per_page in new WP_query (pagination problem)
- Can I turn off write-in tags/taxonomies?
- display posts with same taxonomy term
- Get value in custom field with taxonomy [closed]
- Get second level terms of custom taxonomy
- pre_get_posts with tax_query causes empty result
- restrict_manage_posts not working in 3.3.1
- Can I lock down custom taxonomies on a parent term level, but not a child term?
- get_query_var(‘paged’) always returns empty
- Programatically inserting terms doesn’t update the Taxonomy admin UI
- Allowing specific users to only add posts using certain custom taxomy terms
- Edit tags page for hierarchical taxonomy doesn’t show taxonomies at all depths
- Taxonomy menu with post count and multiple parents
- I want to load post content by categories using Ajax
- Sort Custom Post Type Archive by Taxonomy Term [duplicate]
- Including all terms in wordpress tax_query
- Get only the first term by taxonomy
- Taxonomy Templates… by hierarchical level?
- Exclude specific slug in ‘get_terms’