The API worked. The books did not. A clean REST interface with pretty JSON still leaves accounting stitching exports for three days to answer one question - what happened to this payment across every rail and every failure path. ERP-grade APIs treat the contract as a shared language with finance.
Stripe, OpenAI, and Google shipped protocols that let AI agents complete purchases inside a conversation. The rails are already fast enough. The problem is that fraud detection was architected around a human clicking buy on a trusted surface, and agents break that assumption.
Your bank says it is "ISO 20022 ready" for the November 22 cutover. Check the docs and it is usually a translation layer - MT to MX at the SWIFT boundary, MX back to MT inside. That is compliant, and it quietly throws away the structured data that was the whole point.
Subscription billing has two bad options today - store the card or chase a manual approval every cycle. Variable recurring payments add a third: pre-authorized variable amounts with limits enforced by the rail. The UK is building it now, and the lesson for everyone else is about regulatory cycles, not technology.
The CFO sees "save 3 percent on transactions" and the math looks obvious. Treasury sees continuous settlement at 3 AM and a reconciliation process built for batch. Before you switch to account-to-account, count the operating cost the savings slide leaves out.
Payments runs on documents - checks, wires, invoices, KYC files - and the OCR that reads them chokes on handwriting and damage. DeepSeek-OCR processes a page as roughly 100 visual tokens instead of a thousand text tokens, and it is open source. The headline accuracy comes with a compression ceiling worth knowing.