With FedNow seemingly using a 'a bespoke flavor of the ISO 20022 specification' (https://news.ycombinator.com/item?id=36805571), I wanted to put up a breakdown of my experience with it. I think that it's a pretty handy format to be familiar with, and is quite simple to work with too.
If the Fed or participating banks decide to open up the system like European banks have done so, it can be handy to get familiar with it for us financial hackers out there!