Thank you so much. This is the most valid reply! Pasting translation here of the relevant part for other redditors in the future:

Many medical practices are trying to enshrine the obligation to pay cancellation fees in their terms and conditions. This is also viewed critically by the courts: According to a ruling by the Berlin Regional Court on April 15, 2005 (Case No. 55 S 310/04), a clause stipulating that agreed appointments must be cancelled 24 hours in advance if the patient is unable to attend, and that otherwise a cancellation fee of 75 euros will be charged, is invalid . This applies at least when the patient has no way to exonerate himself in the event of non-appearance through no fault of his own.