capabilities

When assigning capabilities to ‘capabilities’ argument of register_taxonomy() you need to assign the capability and not the role! so use capabilities that only a specific role has eg: ‘capabilities’ => array ( ‘manage_terms’ => ‘manage_options’, //by default only admin ‘edit_terms’ => ‘manage_options’, ‘delete_terms’ => ‘manage_options’, ‘assign_terms’ => ‘edit_posts’ // means administrator’, ‘editor’, ‘author’, ‘contributor’ )

Just like CPT capabilities those of taxonomy are also customizable, in register_taxonomy(): capabilities ‘manage_terms’ – ‘manage_categories’ ‘edit_terms’ – ‘manage_categories’ ‘delete_terms’ – ‘manage_categories’ ‘assign_terms’ – ‘edit_posts’ Since your authors only have edit_posts it works as you observe — they can assign existing terms, but not create them. You can customize capabilities for taxonomy in question and … Read more