You're the on-call engineer at a Nigerian neobank. You ride on a sponsor bank for actual money movement, you hold customer funds For Benefit Of (FBO) at the sponsor, and every deposit / withdrawal / inter-wallet transfer eventually maps to a settlement call against their API. At 10:14 WAT on a Tuesday, the sponsor bank's API starts returning 503 Service Unavailable on every call. Their status page says nothing yet. The first 5,000 customer withdrawals of the morning are now stuck in an in-flight state, and traffic to your app is climbing toward the lunchtime peak. This incident isn't on a Wikipedia page; it's the kind of incident every neobank engineer lives through and never quite writes up. You're going to walk it now from inside, the way the actual call sheet runs.