How PayPal Scales Payments: The Architecture of Global Trust

In this guide, we explore system. Your transaction is pending. A timeout occurs. Now you're staring at a screen wondering if you just paid $1,000 twice or if your money vanished into a digital void. For most apps, a 500 error is a nuisance; for a payment processor, it is a potential regulatory nightmare and a total loss of customer trust. Table of Contents The Brutal Reality of Payment Systems The Macro Architecture: From Monolith to Microservices Solving the Double-Spend: Idempotency Keys The L