Bundles are repeatable groups of fields.
Unfortunately it's not (yet) possible to add file, image, repeatable fields to a bundle. This is because these fields are Vue fields, and Vue will not update when the fields are added (via AJAX). This is a known bug in Cuztom, if you know a solution, please open an issue on Github or contact me.
$box = register_cuztom_meta_box( $id, $post_type, array( 'fields' => array( array( 'id' => '_data_bundle', 'type' => 'bundle', 'fields' => array( // Fields ) ), ... ) ) );
Updated over 5 years ago