Before posting, I already tried on different laptops, mobile device, different browsers and app, using different account, new account, etc, everything returning error at last step.
Called them, they helped me to setup a reservation, but they cannot help on the purchase error, and cannot buy ticket through the call, they sells 30 days in advance.
It's a spring break week, just checking if anyone experiencing the same issue. April 7th is Friday, not sure if they locked it. Worse case, we can still buy the ticket onsite on the day as we have reservation.