Fiserv, Bottomline, and a core banking system each work fine alone. Wiring them into one payment chain is where projects go to die - and the difference between the ones that survive and the ones that become expensive lessons is a handful of boring resilience patterns.
RTP cleared $246 billion in 2024 and the headlines said instant payments had arrived. The average transaction sizes tell a quieter story - this is high-value institutional money on a faster rail, not the consumer revolution that was promised.
Fraud-prevention AI demos dazzle, then meet reality - the bank's wire, ACH, card, and instant-rail data live in separate systems. A model that cannot see the whole customer cannot catch a fraudster who moves across all of them.
An $8M deal chopped into 16 payments because one bank used FedNow. With TCH-RTP at a $10M limit and FedNow at $500K, transaction size is quietly deciding which rail a corporate treasurer can use.
Most banks modernize core-first and treat compliance as the finish line. With Fedwire going ISO 20022-native in July 2025, that order is exactly backwards - compliance is the foundation, not the finish.
A build note from a RAG document system tested on real content. The retrieval was the easy part; the document lifecycle - incremental add/delete and domain separation - was the real work.