The post describes how to create a simple version of the client, but if you're interested in the topic, you can find a production-ready, battle-tested Golang package here: https://github.com/moov-io/iso8583-connection.
And to understand how the whole e2e flow works starting from the seller and finishing with issuer authorizeing the transaction, you can check a demo project here: https://github.com/alovak/cardflow-playground
Never did I think I'd see somebody I know personally hit the front page of HN... hope you and the rest of the Moov crew are doing well! I got to see these libraries in action (and deal with some mutual TLS auth issues) during my time helping out with connectivity to the card networks' sandbox environments. Things were working very smoothly even 2+ years ago so "battle-tested" is probably an understatement at this point :))