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# `x402/express.mpp` \[Add MPP to an x402 Express server]

Wraps the official x402 Express middleware so one route accepts MPP and x402 Credentials.

Requires `@x402/core` and `@x402/express` 2.22 or later, Express 5 or later, and viem 2.54 or later.

## Usage

```ts [server.ts]
import { HTTPFacilitatorClient, type RoutesConfig, x402ResourceServer } from '@x402/core/server'
import { ExactEvmScheme } from '@x402/evm/exact/server'
import express from 'express'
import { mpp } from 'mppx/x402/express'

const facilitator = new HTTPFacilitatorClient({
  url: 'https://x402.org/facilitator',
})
const server = new x402ResourceServer(facilitator).register(
  'eip155:84532',
  new ExactEvmScheme(),
)
const routes = {
  'GET /api/data': {
    accepts: {
      network: 'eip155:84532',
      payTo: '0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266',
      price: '$0.01',
      scheme: 'exact',
    },
    description: 'Premium data access',
    mimeType: 'application/json',
  },
} satisfies RoutesConfig

const app = express()
app.use(mpp(routes, server, { // [!code hl]
  secretKey: process.env.MPP_SECRET_KEY!,
}))
app.get('/api/data', (_request, response) => {
  response.json({ data: 'premium content' })
})
```

The wrapper leaves x402 response buffering, hooks, handler cancellation, verification, and settlement with the official adapter. A request containing both an MPP Credential and an x402 payment signature returns `400`.

## Return type

```ts
type ReturnType = RequestHandler
```

## Parameters

### config

* **Type:** `{ paywallConfig?: PaywallConfig; realm?: string; secretKey: string }`

MPP Challenge and optional x402 paywall settings. `secretKey` must contain at least 32 bytes.

### routes

* **Type:** `RoutesConfig`

Existing x402 route configuration. The first extension-free EIP-3009 `exact` requirement with valid amount, asset, EVM network, name, recipient, and version fields also produces MPP Tempo and source-chain EVM Challenges.

### server

* **Type:** `x402ResourceServer`

Existing x402 resource server used for requirement metadata, verification, and settlement.