Why Single-Gateway Payment Pipelines Break Under ConcurrencyWhen building enterprise retail and commerce platforms, many engineering teams treat payment processing as a standard REST API call. A point-of-sale (POS) terminal initiates a checkout request, the application layer sends the payload to a payment service provider (PSP), and the resulting network response (200 OK, 402 Declined, or 504 Gateway Timeout) determines order completion.It feels pretty simple, but there are three particular systemic weaknesses that need to be considered during high transactional traffic: