Почему не работает проверка поля на загрузку файла?

Question

[Minusator]

Доброго дня!

Пытаюсь проверить поле загрузки Gif файла (image_image) в форме перед отправкой.
Поля формы

public function structure(){
            return [
                "title" => [
                    "type" => "field",
                    "name" => "title",
                    "label" => __("Title", "plugin-name"),
                    "field_type" => "text",
                    "rules" => [
                       "required",
                    ]
                ],
               "gif" => [
                    "type" => "group",
                    "name" => "gif",
                    "fields" => [
                        "image_image" => [
                            "type" => "field",
                            "name" => "image_image",
                            "label" => __("Browse File", "plugin-name"),
                            "field_type" => "file",
                            "rules" => [
                                "extensions" => "gif,mp4",
                                "maxSize" => zf_get_option("zombify_max_upload_size") / 1024
                            ],
                            "use_as_featured" => true
                        ]
                     ]
                ]
            ];
        }

Проверка

class BBC_ZF_Tweaks {
	public static function edit_gif_quiz_structure( $structure ) {
		$structure[ 'gif/image_image' ] = true;

		return $structure;
	}

}

add_filter( 'plugin-name_structure_gif', array( 'BBC_ZF_Tweaks', 'edit_gif_quiz_structure' ), 10, 1 );