You don't have to get reserved parking, just pay there at the machine. It takes card.
Why is the reservation system necessary / why do the reservations sell out quickly during wet season? Because the park has a pretty tiny day use parking lot and I'm sure before the reservation system they'd have a bunch of disappointed people who'd either park illegally around Sveadal or have to drive 30 minutes plus to get to another park. Why is the reservation system clunky and difficult to use? Because it's a county park and I don't think they were able to get Jony Ive to do the design for it.
2020 update. Need to reserve before hand
Day use is a drive in option. You pay at the machine. No need for reservations.
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