I had convinced myself I'd need to chat with MS today to make the reservation, but then ... I was lucky late yesterday (well actually today at 1 AM Eastern time) and finally booked the reservation I wanted for November. It was via Safari on my iPhone. Tested it today on Safari/iPhone and back to the seven dwarves error screen. I had tried earlier yesterday using Chrome in Incognito mode with no success. So I'm convinced the better chances online are late at night/overnight/early in the morning. Glad I don't have to try again any time soon.