Payments & Financial Systems

How real products safely move money: gateway integration, why the webhook is the source of truth (not the browser redirect), idempotency, and the double-entry ledger patterns behind every serious billing system.

11 lessons

Study 39 cards for this domain

Beginner

How online payments actually workBeginner4 min read·Not startedWebhooks are the source of truth, not the redirectBeginner3 min read·Not startedNever store money as a floatBeginner3 min read·Not startedPayment states as a lifecycle, not a booleanBeginner3 min read·Not started

Intermediate

Idempotency in payment systemsIntermediate3 min read·Not startedVerifying webhook signatures correctlyIntermediate3 min read·Not startedSubscription billing patternsIntermediate3 min read·Not startedRefunds, disputes, and reconciliationIntermediate3 min read·Not started

Advanced

Double-entry accounting for engineersAdvanced3 min read·Not startedImmutable ledger designAdvanced3 min read·Not startedDesigning a payment webhook handler end to endAdvanced4 min read·Not started