If Germany companies work like UK companies, you can setup a company, pay corp tax on your profits and leave the money in the company.

Then a in a year or two you can take the remaining money out using dividends.

Fundamentally, it's a tax inefficient way of doing things, but it's the company making the money, while you're only earning whatever smaller amount you pay yourself.

Bit late for this income, as you've already been paid.