To add a bit more detail: as far as I understand it (and I am no lawyer) the concept of an Abmahnung is that you notify someone of their (supposed) legal transgression, and give them the option to stop their behaviour and reimburse your costs (lawyer's fees and damages) to avoid going to court. For copyright claims in particular, it may be difficult to claim large damages, but sometimes the right holders collude with their lawyers by demanding the reimbursement of non-existent fees instead, which they then split as profits. This is illegal, as you are only allowed to claim costs that you have actually paid.

A (somewhat dated) example at [1] (german).

[1] https://www.lawblog.de/archives/2009/11/17/abmahnanwalte-ver...