Payments

Mental model

Payment systems are several systems agreeing about money: the card network, the processor, your database, and accounting. Treat every state change like a ledger entry, use idempotency keys on every request, and reconcile against the processor daily.

How to study Payments

Begin by restating the mental model in your own words, then connect it to a concrete system you have built or operated. Name the mechanism, the constraint it addresses, and the trade-off it introduces. Use Stripe Payments documentation to check details, but close the source before writing your explanation. Retrieval is the learning step; rereading is only preparation.

Next, compare Payments with Idempotency. Ask what changes in correctness, latency, resource use, operability, and failure recovery. Complete Idempotent charge and preserve the command, input, output, and one failed attempt as evidence. Finish by explaining the idea without jargon to someone who has not studied the track.

Proof of understanding

• Explain the mechanism from first principles and identify the state it reads or changes.
• Give one situation where the concept is the right choice and one where it is not.
• Predict a realistic failure mode before running the drill, then compare the prediction with evidence.
• Connect the result to a roadmap or build artifact instead of treating the concept as isolated trivia.

Learn from primary sources

• Stripe Payments documentation (doc)

Practice and explain it back

Review prompts

• The charge succeeded at the processor but your service crashed before writing the row. What mechanism recovers this, and why is a retry not enough?

Build evidence

Use a roadmap capstone to turn this concept into working evidence.

Learning paths

None assigned yet.