400 € on which I had to pay 10000€ tax, because Germany has flat rate social insurance fees for freelancers, almost independent of your actual income. It's an absolutely horrible country
In Poland a sole-freelancer also has to pay a flat rate of 1200zl (300 euros) per month for social security + income tax (aprox. 15%), but if you already have a job then you only need to pay income tax of the freelancer work and no social security for it (since you already pay social security from the main job). Isnt it the same in Germany?
Do you have a main job?