Flight is tomorrow. UA website has been offering $35 wi-fi for the SFO->HKG route. I had to get some work done so was planning to sign up for it before departure. Today, however, the option is greyed out for the SFO->HKG leg, but only shows available for the return leg. Does that mean no Wi-Fi is available for that flight? Or is it "sold-out"?

Will I be able to purchase in-flight?

Also, anyone knows how the charge shows up if Wi-Fi is purchased in-flight? Wondering if it will qualify for Amex Plat credit.