clawhub-x402-payments

# ClawHub x402 Payments (USDC via PayAI + DHM via EVVM)

This skill documents the two x402 payment flows in the NHS EVVM / ClawHub app: **USDC via PayAI Echo** and **DHM via EVVM native**. Reference implementation lives in this repo.

## Reference paths

| Flow | Client UI | Server / config |
|------|-----------|------------------|
| USDC (PayAI) | `frontend/src/components/sections/USDCX402TestSection.tsx` | Config: `frontend/src/config/contracts.ts` (X402_USDC_ECHO_URL, USDC_BASE_SEPOLIA) |
| DHM (EVVM) | `frontend/src/components/sections/X402TestSection.tsx` | `server/src/index.ts` (GET 402, POST /payments/evvm/dhm) |
| EVVM sign | `frontend/src/lib/evvmSign.ts` | — |

Chain: **Base Sepolia** (chainId 84532).

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## Flow 1: USDC x402 via PayAI Echo

PayAI returns **402** with an `accepts` array (not `options`). Client picks a USDC option, builds EIP-3009 `TransferWithAuthorization`, signs EIP-712, sends signature in `PAYMENT-SIGNATURE` header, retries the same URL; server returns 200 and may set `PAYMENT-RESPONSE` header with result (e.g. `transaction` hash).

### Client steps

1. **Request resource**  
   `GET <Echo URL>` (e.g. `https://x402.payai.network/api/base-sepolia/paid-content`).

2. **Parse 402**  
   - Prefer `PAYMENT-REQUIRED` response header (base64-encoded JSON).  
   - Fallback: response body may be JSON with `accepts` array.  
   - Type: `{ x402Version?, error?, resource?, accepts: Array<{ scheme, network, amount, asset, payTo, maxTimeoutSeconds?, extra? }> }`.

3. **Pick USDC option**  
   - From `accepts`, choose entry where `asset` matches USDC on Base Sepolia or `extra.name === "USDC"`.  
   - Use `amount`, `asset`, `payTo`, `extra.name` / `extra.version` for EIP-712.

4. **Build EIP-3009 authorization**  
   - Domain: `name` = `extra?.name ?? "USDC"`, `version` = `extra?.version ?? "2"`, `chainId` = 84532, `verifyingContract` = `asset`.  
   - Type: `TransferWithAuthorization`: `from`, `to`, `value`, `validAfter` (0), `validBefore` (e.g. now...