I mean, not sure what ‘fully realtime’ means, but there was probably at least 3 hours between the change and the onboard purchase, and an additional almost 48 hours before it was put through (based on the time I received the receipt from UA, which was within a couple of minutes of receiving a purchase notification from the card issuer). I have to assume that despite a confirmation of the change, UAs system never actually made it, since that should be plenty of time for a change like that to process - plenty of companies do that essentially instantly.

if they aren’t able to make a change like that after check in, that’s one thing, but there shouldn’t be a facility to ‘pretend’ to do so, and there should be full disclosure somewhere. Especially in that case, but even if not, I’m not sure where the legal authority even exists to authorize onboard purchases when checking in with an agent. OLCI on the app offers the ability to review/change the card at time of check in, which gives authorization, as does a kiosk, I believe. How that happens with an agent is beyond me (unless perhaps the agents can request it, but at least in my case, that was not done).

the amount, in this case small and not a big deal, isn’t the point - the fact that a major corporation that has a card on file, and feels they can take a purchase without an authorization to do it via that payment method is the issue for me.