ARC renewal — can I do it fully online, or must I visit immigration in person?

My alien registration card expires next month and I've been trying to book a renewal slot on HiKorea for two weeks. Every time I select my immigration office, it says no reservations are available. Is it actually possible to renew the ARC entirely online now, or do I still have to show up in person with the documents? If anyone has done it recently in the Ansan area, what was the real process?