No the OP, but Scheinselbstständigkeit is one of the scarecrows of freelancers and their clients in Germany. It is actually not very difficult, but in certain cases it is very limiting. If you can read German, here is a handy reference sheet, which is distributed by virtually all tax advisors [1].
[1] https://www.sup-kanzlei.de/fileadmin/user_upload/Scheinselbs...