eBooks do not have page numbers because they are reflowable documents designed to flow over various different screen sizes.
An eBook is basically just one long webpage that is broken up in smaller "pages" by the eReading device or software. Some eReading devices will assign page numbers, but these page numbers can change once the user changes the font size and type. As a result, there are no true page numbers in an eBook and they should be removed from your manuscript prior to submitting them to BookBaby.