Hi @hmlongvo,
Thanks for your message. You’re right, subscribers cannot download the books to read offline, and currently the option to purchase a book is not visible for subscribers.
However, if you’d like to purchase a book, you can email us at support@razeware.com with the name of the book you’d like and we can sort this out for you no problem by creating a custom order for you.
Please let me know if there’s anything else you need :]