Question about selling via Amazon.de and System participation requirements

Hello everyone, I just registered for a LUCID number – part of the packaging law in Germany, but I am not sure whether my product is subject to system participation or not. I do not fully understand this part. I am selling my own books, but obviously when sending them I will put them in a paper envelope or cardboard sheet. So do I have to apply for System participation because of it?

Any help will be much appreciated! Thank you!!!