No fee here in MK (RingGo). And no need to register a payment card either, you can use Google Pay with whatever card you have it set to at the time.
Also it's very convenient in that you can increase your parking time remotely (up to the maximum). So you can ask it to remind you just before it runs out and then if you're not back at the car yet you can add some more time. Not seen any cash or card payment scheme that makes doing that easy. Not having to worry about not buying enough time up front actually saves YOU money!
nib