Why it matters
A card payment is not one message; it is a sequence of events that can run over days:
- an authorisation;
- perhaps an adjustment;
- a batch close;
- clearing;
- settlement between banks;
- funding of the merchant;
- the cardholder's statement;
- sometimes a dispute.
Bugs and test gaps hide between these steps:
- a reversal that never arrives;
- a hold that is never released;
- a batch that does not balance;
- a chargeback nobody expected.