While the reason is not necessarily correct (although it’s more of an over simplification than an outright error) the terminal needs to have the correct time if

While the reason is not necessarily correct (although it’s more of an over simplification than an outright error) the terminal needs to have the correct time if not the transaction would not be processed for a myriad of reasons. The issue is that in the vast chain of networks that a single transaction flows through you have multiple NTP servers each of them taking their own time form a different source which is often backed by GPS. If GPS services are disrupted globally this would cause payment networks to break down. Yes there would be a way to recover from it and move away from GPS but you are still missing the point on day-0 of a GPS blackout the global financial system would go down and it would be a mess and it wouldn’t be a mess that is easily sorted…