Appendix B — Payment Flow Diagrams

Every core flow in the book, in one place. Each diagram is the canonical version — the chapter pointer takes you back to the full story. All diagrams are Mermaid; copy them freely into your own docs.

The Canonical Payment Flow

The four universal stages every rail follows — cards, bank transfers, wallets, stablecoins. See Chapter 4.

Card Payment Lifecycle

Authorization, capture, and settlement as a state machine — including the path where an auth simply expires. See Chapter 9.

3DS: Frictionless vs Challenge

The fork that decides whether your customer sees friction — and who eats the fraud loss. See Chapter 11.

Tokenization Paths

Three ways a PAN becomes a safer credential — with very different portability. See Chapter 12.

Chargeback & Representment Lifecycle

Where a dispute can go, and who pays at each exit. See Chapter 13.

Dunning Retry Ladder

What a good recovery system does after a failed renewal charge. See Chapter 15.

Virtual Account Flow

Why a VA turns "who paid me?" from a guessing game into a lookup. See Chapter 18.

QR / Pay-by-Scan Flow

QR is an interface for capturing intent — the money still moves on a bank or wallet rail underneath. See Chapter 19.

Direct Debit Mandate Lifecycle

Pull payments are cheap and sticky — and revocable long after you shipped the goods. See Chapter 20.

Carrier Billing Flow

The telco is issuer, acquirer, and collections department all at once. See Chapter 21.

Stablecoin Payment Lifecycle

The transfer is fast and final; the choke points sit at the edges. See Chapter 28.

Intelligent Payment Routing

Orchestration in one picture: route by rules, retry on failure, fail gracefully. See Chapter 32.

The Four-Layer Agentic Payment Stack

When software spends money, identity comes first and settlement comes last — invert the order and you're billing strangers. See Chapter 33.