Payments - full curriculum

Separate the four different events that 'the payment went through' collapses into one, and learn who in the chain is entitled to say no.

Answer 'which provider' only after answering what kind of money flow this is, where it starts, where it lands, and who is legally selling.

Take one real payment, and know exactly which parts of it an attacker controls.

The module this subject is actually about: what has to be true in your own tables before you are entitled to call an order paid.

Money that arrives again without anyone clicking anything, on two rails that authorise it in completely different ways.

The declines that were recoverable and you lost anyway, and the money that gets taken back after you have already delivered.

Money that passes through you on its way to somebody else, and money spent by something that is not a person.