Since it is decisive how your target country (here Germany) classifies someone as private or commercial, the German Law applies.
The Central Packaging Register(ZSVR) defines commercial sales as follows:
“Anyone who has registered or has to register their self-employment as a business, or anyone who generates income from commercial activities, independent work or agriculture and forestry within the meaning of German income tax law, is operating commercially within the meaning of the Verpackungsgesetz (Packaging Act). Even an individual who claims losses against taxes owing to their activity or computes profit from agriculture and forestry on the basis of average rates (section 13a (6) EStG (Income Tax Act)) is operating commercially. Further information can be found in our informational booklet on commercial placing onto the German market."
FAQ: Commercial initial distribution https://www.verpackungsregister.org/fileadmin/files/Themenpapiere/Subject-specific-paper_overview-for-small-and-micro-distributors.pdf
If you are still convinced that you are selling privately, or you do not have a corresponding tax number, please contact your marketplace.
If you are obliged under the above definition, these three obligations apply:
Obligation 1: Licensing (also called system participation). Conclude a licensing agreement with a dual system (such as Interseroh+ via Lizenzero ).
Obligation 2: Registration. Register with the Central Packaging Register (ZSVR) in the LUCID register.
Obligation 3: The data report. Enter the name of your dual system (Interseroh+ if you license via Lizenzero) and the reported packaging volumes in your LUCID account.