UPDATE: Just made my appointment online.
For anyone struggling to get one, log in after 9 am on a business day and keep refreshing the calendar in 10-min intervals until you see some green boxes appear magically in the same month. Around 9:30 am, I had the option to choose between multiple timeslots from a choice of 3 days (that were supposed to be fully booked).
Scheduling an appointment is supposed to be a FREE service. Don’t give these crooks a cent above the biometric fee you’ve already paid!