A zyBook code uniquely identifies a particular zyBook, typically corresponding to a specific class offering at a school. Instructors can mix and configure zyBook content, so every class' zyBook may be unique. Typically, instructors provide their class' unique zyBook code in a syllabus or in a class announcement. A zyBook code usually looks like this: YourUnivCS101SmithSpring2019 (just an example).
After signing in at zybooks.com, a student can enter their zyBook code to be taken to their class' zyBook, where the student can then subscribe.
If your zyBook code is unrecognized, notify your instructor so they can correct the code. Also email email@example.com with your instructor's name, the zyBook code, and where you got the code, so we can help remedy the issue before other students have problems too.