It’s a lot more complicated and nuanced than that. The API docs you link too are for an API that covers a tiny fraction of what can be expressed in the actual ISO 8583 messages which are the real “API” of the card networks. The docs for those are hundreds of pages long.
Plus you need to analyse how the different messages types and sequence of messages interact with the transaction processing rules, which are also hundreds of pages long.
Suffice to say, the entire system is insanely complicated, and just about everyone out there implements it all incorrectly, with the whole system on working because partners are only allowed to complain about the insanity if they actually loose money. Until that point they’re expected to just handle everything as best they can.
