The same Shaila is about a soda machine. The Minchas Yitzchok discusses it. He included references to Shevisas Keilim. I think he was Mattir. My question here is if you will Assur it, whose Shabbos is the issue? The buyer? Seller? Server? Bank? PayPal server? PayPal bank?
The whole Issur is a Takana from Nechemia not to buy and sell. The question is if it applies here in the first place, since you aren’t making any transactions. I never heard of an Issur of Kinyan Sadeh on Shabbos. There does remain the problem of S’char Shabbos (which would probably go by the seller’s time zone). However, even that might only be through actually doing something. It is Muttar to pay after Shabbos for something that you took on Shabbos.
If you want to avoid it there is a free project holyclock dot com that disables your site on Shabbos, which I got from asite that WIY linked to (Reb Shlomo Kluger’s Sefarim).
Being that Torah discussions on this site are Lehagdil Torah Ulehadira, it is ridiculous to yell at someone for posting his thoughts on Halachic issues.