# Sample POS lifecycle

{% @mermaid/diagram content="sequenceDiagram
autonumber

```
participant app as Xumm App
actor user as End user
participant frontend as Your app Frontend
participant backend as Your app Backend
participant xumm as Xumm Backend
participant xrpl as XRP Ledger (RPC)

user-->>frontend: "I want to pay"
frontend->>backend: Amount typed & sent<br />to initiate pament flow

critical Craft Xumm payload
    Note over backend: XRPL Transaction Template with<br />destination account & currency<br />and stable coin amount to pay.
end
backend->>frontend: Payload returned<br />Persist the UUID in your own database for reference.<br />Forward the payload JSON to your frontend.

critical Construct payload screen
    Note over frontend: Use the payload information to update the UI<br />Render the `refs.qr_png` as image (QR to scan)<br />Subscribe to the `refs.websocket_status` URL<br />for live status updates.
end

par Backend, Frontend and End user react in parallel
    frontend->>user: Show QR to pay with Xumm<br />Shows "Waiting for QR Scan"
    rect rgb(240, 220, 225)
        activate user
            user->>app: Scans QR, opens sign request
        deactivate user
    end
    xumm->>frontend: Sends `opened: true` message over WebSocket
    frontend->>user: Display "Waiting for payment"
end

xumm->>app: "Sign request" (payment approval screen) rendered for end user
activate app
par Sign procedure
    rect rgb(240, 220, 225
        activate user
            user->>app: Approves "Sign request" (makes payment)
        deactivate user
    end
    app->>+xrpl: Transaction submitted to the XRP Ledger
end

deactivate app

xrpl->>-app: Verifies payment & returns status (successful / failed)

xumm->>frontend: Sends `signed: true` (accepted) or `signed: false` (rejected) message over WebSocket
frontend->>user: Display "Confirming payment..." (pending...)<br />or "Payment cancelled" (allow retry?)

xumm->>backend: Sends Webhook with transaction information
backend->>xumm: Verify payload status & transaction hash
backend->>xrpl: Verify transaction outcome
Note over backend,xrpl: Check if the transaction is successful and<br />the `delivered_amount` matches the<br />requested currency and amount.
backend->>frontend: Update payment status

frontend->>user: Payment successful, ... / Payment failed, ..." %}
```


---

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