Interesting point that banks actually tolerate a lot more eventual consistency than most software that just use a billing backend ever do.
Stuff like 503-ing a SaaS request because the billing system was down and you couldn’t check for limits, could absolutely be locally cached and eventual consistency would hurt very little. Unless your cost is quite high, I would much rather prefer to keep the API up and deal with the over-usage later.
If you check out with a credit card, even if everything looked good then, the seller might not see the money for days or might never receive it at all.