Just curious, could you just give it away for free or do they also have some value that will be taxed even though you didn't get any money?
We've had a similar situation happening and it took quite some legal fees to ensure we had all answers ready and in writing before the tax authority would start to ask their questions. It's a complex situation.
Another sad thing is, you can easily get buried in the costs of Legal/Tax advisor costs even for some simple stuff.
That is why sometimes its better not to 'entreprendre' anything while living in Germany. The system is setup in a way to make you work full-time for corps.