Every day after 6 Pm they turn off the availability and the next day at 8 AM it comes back. So check tomorrow morning. I've seen this every day on my apple store app where after 6 pm it disables and at 8 am it re-enables it.
Why would they do that when the store closes at 9pm. Seems counterproductive if someone is looking for stock to buy between 6pm and 9pm when they get off work.