> For the complete documentation index, see [llms.txt](https://metya.gitbook.io/metya/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://metya.gitbook.io/metya/product-and-architecture/key-diagrams.md).

# Key diagrams

System Overview Architecture Diagram

* Three layers: User (App / Live / Tasks) → PayFi (Card / Clearing & Settlement / Risk) → On-chain (Contract Suite / Anchors).
* Highlight the event bus, ledger, KYC/AML, and merchant portal placement.

Sequence Diagram: Top-up to Spend

* Top-up → FX → Ledger Posting → Auth → Capture → Anchoring → Rebates

Swimlane Diagram: Merchant Quest → Issuance → Settlement

* Five lanes: Merchant, User, Risk Control, Contracts, Clearing & Settlement.

DID/NFT Social Card & Rights Linkage Diagram

* DID → Reputation → Social Card → Rights (Membership / Fee Discounts / Limits / Allowlist).

Anti-Fraud / Risk Signal Stack Diagram

* Pre / During / Post controls with signal sources: device, behavior, MCC, geography, history.

Public KPI Dashboard Examples

* MAPU, Card Activation Rate, Merchant GMV, Repurchase Rate, Net Demand Curve.