No, it would not be. De livre isn't a thing. Du livre or des livres are the only options. (Both livre forms sound the same)
De, du (de le), and des (de les) are pronounced very differently. Des is day, du is do, and de is kinda like ew(have google translate pronounce it). Des gets tricky when followed by a vowel sound. Because it's s is surrounded by vowel sounds, it can also be dez. This is a rule for s's in french, not just this case.
I had the same problem at first, but to be fair, duo can't know if you did a typo or you actualy didn't know the right spell. Anywhere else they assume it's the former, but in a training program, they have to lean more to the latter to make sure you're learning the spelling as well.
Get used to read what you wrote once, before you submit. That's what I ended up doing and haven't loose a heart because of this ever since.