Why it matters
A card is a key to someone's money, and whose money and when it moves shapes everything else:
- which messages are sent;
- whether a PIN is needed;
- whether the terminal may offer cashback;
- how a refund works;
- what happens in a dispute;
- how a test plan must look.
Getting the product model wrong is how a debit terminal ends up sending credit-style authorisations that are never cleared.