There are a few reasons why you may not be seeing the eTextbook for your course.
You are trying to access the e-book from an incompatible device
If an eTextbook is available in your Sapling Learning course, you can always view it or purchase it within a web browser on a desktop or laptop computer. Once purchased, you can always read the eTextbook within the Sapling App on an iPad (see the Resources section of the Sapling App). Some newer Sapling e-books are also available to be read offline using a mobile device. However, the majority of eTextbooks offered are not yet available for iPhone or Android devices.