Sometimes if a book does not have a valid ISBN barcode from the publisher it will not scan. Then you would just need to add the title manually.
There are a few different ways to manually enter titles into your library. On the app, simply type in the ISBN (or any value, you can use N/A for titles without an ISBN), and the title of the book, then hit Add.
On the website, From Grow and Manage in the Library, enter the ISBN into the text box labeled Add Title to Library Using ISBN. Or you can click the green plus sign, which will create a blank item, then you can edit that item to add all the info. The book will show up in the library as “No Title Available” – if you have your library sorted by Title alphabetically (using the little arrows on the top blue bar) That blank book should show up right at the top. Then you can click edit (to the left) and add all the information.