Central bank instant payment system. The US has FedNow, and has had it for almost 3 years. It costs a few pennies to move up to $10M per XML message.

Brazil's Pix costs ~$10M/year to run: https://whatispix.com/

This is much cheaper than the entire credit card ecosystem skimming ~3% off of the economy. Efficiency!

FedNow Is Live - https://news.ycombinator.com/item?id=36801491 - July 2023 (1022 comments)

Walmart is currently trialing it to save $3B-$7B a year in interchange fees. No crypto, just XML messages through a mainframe at the Federal Reserve with a 20 second SLA.

> “It surprised me,” Henry said of adoption of Walmart’s first iteration of pay-by-bank, which is available online but hasn’t been marketed to customers. “It’s certainly surpassed our expectations of the amount of customers that have registered and actually use the payment type.”

> Walmart’s upgraded pay-by-bank offering will be rolled out in 2025. The transactions will occur over bank technology provider Fiserv’s NOW Network, which integrates with The Clearing House’s Real Time Payments network and the Federal Reserve’s FedNow. Until now, large retailers hesitated to launch real time payment options because many banks were not connected to an instant settlement system, meaning their customers would not be able to use the product. NOW Network aims to connect to as many banks as possible to reach 100% of deposit accounts by combining its own network with RTP and FedNow.

Walmart Plans Instant Bank Payments, Cutting Out Card Networks - https://news.ycombinator.com/item?id=41593450 - September 2024 (3 comments)

https://news.ycombinator.com/item?id=49433164 (citations)

(as of this comment, there are 100+ instant payment systems live across the world; we should assume that all countries will eventually have an instant payment system, or integrate with someone else's)

https://www.pymnts.com/wp-content/uploads/2026/09/PYMNTS-Int... [pdf] (September 2026 revision)

> Walmart is currently trialing it to save $3B-$7B a year in interchange fees. No crypto, just XML messages through a mainframe at the Federal Reserve with a 20 second SLA.

Please tell your user that this SLA is much too high for many purposes. A cafe or such would lose a ton of money if every transaction took 20 seconds longer to conduct.