How do I add spine text to my hardcover book?

Adding spine text is easy!

iOS:
You can add spine text from the 'Settings' menu on the 'Book View' screen. 

Step 1:

Step 2:

Android:

After selecting a hardcover book, a dialog box will pop up prompting you to add text to the spine of your book. Simply add the text you wish and then tap 'Set Spine Text' to continue to checkout. 

(Spine text is not available for softcover books.)