Period: 2022.11.22 13:00 - 2022.12.14 Maintenance
Event description says that you can pre-register for Megu and Usa, but as far as I understand in reality you just subscribe to extra emails in exchange for coupon (maybe the classes will be available 1 week ahead for pre-registered users or something in that line, it's totally unclear from the event itself).
Pre-registration page can be found HERE.
No idea why they have complicated things so much, but you need to enter your email, then confirm it using OTP sent to your email, agree to emails and press the pre-register (Red) button to get your coupon code.
Period: 2022.11.23 19:00 - 2022.11.30 23:59
Period: 2022.11.23 Maintenance - 2022.12.06 23:59
Period: 2022.11.23 Maintenance - 2022.12.07 Maintenance
Sale periods: 2022.11.23 Maintenance - 2022.12.07 Maintenance/2022.12.28 Maintenance
Sale period: 2022.11.23 03:00 - 2022.12.02 03:00