We're not disagreeing. These are (university) hospitals and corporations. I've seen numbers indicating that 70% to 80% of blood donations in Germany are done via the German Red Cross. The Red Cross does not pay money for blood donations.
Pre-COVID the German Red Cross often would have a buffet lunch typically consisting of sandwiches and fruit for donors. Since then they seem to have moved to prepackaged lunches and branded giveaways. But never cash money.
What you can see from that is that a "Aufwandsentschädigung" of ~20€ is pretty common.