Of the eight pages Google currently ranks for "ACH vs RTP vs FedNow", five quote a FedNow limit that has been wrong since November 2025, two still say the RTP cap is $1m, and one claims FedNow only runs between 7am and 7pm. Not one of them names an ISO 20022 message, shows an API payload, or explains why a FedNow "return" is a favour rather than a right. This guide is the version I wanted when I first had to pick a rail per payout for a US treasury product. It covers the four domestic rails a...