To provide an optimal quality sample for books with interactive content, Apple recommends that you supply your own custom sample due to the dynamic, complex nature of an interactive book. However, a custom sample is optional for books with interactive content. To create a custom sample, create a separate .epub file that includes the pages you want in the sample and deliver it within the <assets> block with type="preview". See Apple Books Metadata XML File Annotated in Apple Books Book Package Specification for more information.
Note: Automatically-generated samples are not supported for books with JavaScript interactivity if they are also read aloud.