If you are in possession of a disability parking card, you are entitled to park for an unlimited period of time on public land (in accordance with information sheet point 5.2). The charging of parking fees in public parking lots is governed by local regulations.
However, parking concessions do not apply to privately managed parking areas such as court-ordered bans, parking garages, parking halls, etc.
Therefore, if you received a handling fee, your vehicle was in a privately managed parking area. Depending on the owner's regulations, "free" parking may or may not be tolerated there. However, it cannot be assumed that parking is free for owners of an disability parking card.