> ## Documentation Index
> Fetch the complete documentation index at: https://docs.zennopay.com/llms.txt
> Use this file to discover all available pages before exploring further.

# How Zennopay works

> One picture of the whole system — apps, money, and rails — with links to go deeper.

Zennopay sits between a partner fintech's USD wallet and Southeast Asian QR
rails. The partner pre-funds a USD balance; each payment draws it down, and a
licensed local payout partner delivers local currency to the merchant. The
partner app never leaves the foreground — the whole pay experience is the
native [PaymentSheet](/payments/overview).

```mermaid theme={null}
flowchart LR
    subgraph Partner
        App[Partner app<br/>+ PaymentSheet SDK]
        BE[Partner backend<br/>creates intent HMAC-signed]
    end
    subgraph Zennopay
        API[Zennopay API<br/>mints session token]
        FBO[USD FBO account<br/>pre-funded by partner]
    end
    subgraph Corridor [Destination corridor]
        Rail[Licensed local<br/>payout partner]
        M[Merchant bank account<br/>THB / VND]
    end

    App -- "checkout session" --> BE
    BE -- "HMAC-signed API calls" --> API
    API -- "session token" --> BE
    App -- "scan / confirm / status<br/>(session token)" --> API
    API -- "per-payment drawdown" --> FBO
    FBO -- "USD" --> Rail
    Rail -- "local-currency payout" --> M
```

Three things to hold onto:

1. **One credential.** Your backend signs API calls with a long-lived HMAC
   secret; Zennopay mints the short-lived, single-intent session token your app
   holds. No key pair to generate or register. See
   [Authentication](/authentication).
2. **USD-only custody.** Partner funds sit in a For-Benefit-Of account at
   Zennopay's US banking partner; all FX happens downstream in the payout
   partner network. See [Funds flow](/concepts/funds-flow).
3. **Corridors are locked at intent creation.** Thailand PromptPay
   (`th_promptpay`) and Vietnam VietQR (`vn_vietqr`) are live, each with
   [per-user limits](/fundamentals/limits) Zennopay enforces for you.
   See [Corridors](/concepts/corridors).

## Go deeper

<CardGroup cols={2}>
  <Card title="Make a payment" icon="qrcode" href="/payments/overview">
    The PaymentSheet: one call in, one PaymentResult out.
  </Card>

  <Card title="Build your session endpoint" icon="server" href="/payments/session-endpoint">
    The one backend route every payment starts with.
  </Card>

  <Card title="Funds flow" icon="money-bill-transfer" href="/concepts/funds-flow">
    Pre-fund → FBO → drawdown → local-rail payout.
  </Card>

  <Card title="Settlement & reconciliation" icon="scale-balanced" href="/concepts/settlement">
    Daily cycle, reports, and the audit trail.
  </Card>
</CardGroup>