> ## Documentation Index
> Fetch the complete documentation index at: https://x402-stellar.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Settlement Contract Overview

> Architecture and design decisions of the settlement-verifier Soroban contract

## Overview

The `settlement-verifier` contract is the on-chain anchor for x402 payments on Stellar. It is compiled to WebAssembly targeting `wasm32v1-none` using `soroban-sdk = "26.1.0"` and Rust 1.92.0.

## Live Deployments

| Network             | Contract ID                                                | Explorer Link                                                                                                                      |
| ------------------- | ---------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------- |
| **Stellar Testnet** | `CATZACNU6KVGZXYF7J4O4NLINRKL5FWC2YAQPHTIQMSQPDAJSSOMRUNL` | [View on StellarExpert](https://stellar.expert/explorer/testnet/contract/CATZACNU6KVGZXYF7J4O4NLINRKL5FWC2YAQPHTIQMSQPDAJSSOMRUNL) |

## Core Responsibilities

1. **Replay Protection**:
   Tracks per-payer nonces in persistent contract storage. If an attacker attempts to replay an authorization payload, the contract detects that `provided_nonce != current_nonce + 1` and reverts with error code `4` (`InvalidNonce`).

2. **Atomic Fee Distribution**:
   Transfers funds from the payer to the merchant and collects a protocol fee in basis points (`10,000 bps = 100%`) in a single atomic transaction. Either all transfers succeed or the transaction reverts.

3. **Storage Tiering & TTL Management**:
   * **Instance Storage**: Stores protocol configuration (`Admin`, `FeeBps`, `FeeRecipient`). Automatically renewed during calls.
   * **Persistent Storage**: Stores payer nonces with TTL extension helpers to prevent data eviction while keeping costs predictable.

4. **Structured Event Logging**:
   Emits `SettlementReceipt` and `InitializedEvent` on-chain, allowing off-chain indexers and accounting systems to track payments by topic.