No idea where you bank, but my Visa notifications are instantaneous, so the network is clearly capable of that. I'm with a modern European bank though, I wouldn't be surprised if the mainframe-lowing US banks that do everything via overnight batch jobs are incapable of this.
With that said, there are places which straight up won't send your transaction to the network at purchasing time. Apple[1] is one notable example. They seem to have a cron job that runs at midnight and does billing for that day. This is really annoying if you're buying an expensive Apple product and increase your card limits for one day only.
I've even seen places that do extremely-low-value transactions "on faith" - the transaction is entirely offline, it gets send to the network the next day, and if it is rejected, your card number goes on a blacklist until you visit the company's office in person and settle the debt.
I wouldn't be surprised if your European bank still relies quite heavily on its mainframes. The mainframe offers high availability, reliability, and, contrary to popular belief, high throughput. Batch processing is just one thing they're good at; real-time processing at high speed is another.
Did you meant Apple Card, Apple Pay or the Apple Store?
Visa/MC transactions go through at least four systems (merchant, merchant payment service provider/acquirer, Visa/MC, issuer processor); Amex is merchant acquirer and card issuer in one, so there is no network and accordingly at most three parties involved (merchant, merchant PSP, Amex).
That said, some of my Visa/MC cards have very snappy notifications too. In principle, the issuer or issuer processor will know about the transaction outcome even before the merchant (they're the one responding, after all), and I definitely have some cards where I get the notification at the same time and sometimes before the POS displays "approved".
Even more magical: when sending money to someone I'm physically present with, I hear their notification before the "money sent" animation finished on my own phone
Must be your bank, because both my Visa and MasterCard ping my phone instantaneously, too.
Well thats sort of the thing...with Visa and MC, there is an extra layer or two of the bank or Fidelity Information Services. With Amex, they own the full stack end to end.
Nope. The merchant can choose the level of verification - in some cases, like copying the card with an imprinter [1] or running phone transactions (yes, that is possible - it's called MOTO [2]), it's obviously impossible to check card limits.
Downside of CNP transactions is, the merchant is fully liable for anything from fraud over chargebacks to exceeding limits.
And then you got card-present transactions but the network connectivity is down for whatever reasons... been a while since I messed with that, but at least for German cards you could configure the terminal to store the account details for later submission when connectivity was restored.
[1] https://en.wikipedia.org/wiki/Credit_card_imprinter
[2] https://docs.adyen.com/point-of-sale/mail-and-telephone-orde...