Add MPP to an endpoint

payMiddleware generates MPP challenges by default as part of dual-protocol. No additional configuration is needed for basic MPP support. The configuration below shows the full middleware chain with notes on MPP-specific behaviour.

Dashboard
SDK
cURL

Dashboard support for managing paid endpoints is coming soon. Use the SDK to configure MPP on your routes.

import express from 'express';
import { initialise } from '@prudra/core';
import { walletMiddleware, payMiddleware, vaultMiddleware } from '@prudra/express';

initialise({ apiKey: process.env.PRUDRA_API_KEY! });

const app = express();
app.use(express.json());
app.use(walletMiddleware({ walletId: process.env.BYO_WALLET_ID }));

app.post(
  '/analyse',
  payMiddleware({
    price: '0.05',
    description: 'Document analysis',
    // acceptSessions: true  // uncomment to enable session payments (Pro plan)
  }),
  vaultMiddleware(),
  async (req, res) => {
    // req.payment.protocol is 'mpp' if the agent paid with MPP
    console.log('Paid via:', req.payment!.protocol);

    await req.vault!.addDocument({ result: 'analysis done' }, 'Result');
    await req.vault!.seal('Complete');

    res.json({
      vaultId:   req.vault!.id,
      protocol:  req.payment!.protocol,
      sessionId: req.sessionId ?? null,  // only set for session payments
    });
  }
);

# Without payment — see the WWW-Authenticate header in the 402
curl -i -X POST http://localhost:4001/analyse \
  -H "Content-Type: application/json" \
  -d '{"text": "analyse this"}'

# With stub payment
curl -X POST http://localhost:4001/analyse \
  -H "Content-Type: application/json" \
  -H "X-PAYMENT: stub_payment_accepted" \
  -d '{"text": "analyse this"}'

What the 402 response includes

When a request arrives without payment, the MPP challenge appears in the WWW-Authenticate header:

HTTP/1.1 402 Payment Required
WWW-Authenticate: Payment id="ch_abc123",
  realm="your-api.com",
  method="tempo",
  intent="charge",
  request="eyJhbW91bnQiOiIxMDAwMCIsInJlY2lwaWVudCI6IjB4..."
PAYMENT-REQUIRED: eyJwcmljZSI6IjAuMDUiLCJ...
Cache-Control: no-store
Content-Type: application/problem+json

{
  "type": "https://api.prudra.dev/problems/payment-required",
  "status": 402,
  "title": "Payment Required",
  "detail": "See WWW-Authenticate (MPP) or PAYMENT-REQUIRED (x402)."
}

Both headers are always present. The agent parses the WWW-Authenticate header to get the MPP challenge parameters.

What the 200 response includes

After successful MPP payment:

{
  "vaultId": "vlt_clx1abc123",
  "result": "...",
  "protocol": "mpp",
  "sessionId": null
}

If session payments are enabled (acceptSessions: true) and the agent is starting a new session, the response also includes the X-PRUDRA-SESSION-ID header and sessionId in the body.

payMiddleware options for MPP

Parameter	Type	Required	Description
`price`	string	Yes	Payment amount in USD
`description`	string	No	Human-readable description
`acceptSessions`	boolean	No	Enable session payments (Pro plan). Default: `false`

Error handling

Error	Status	Cause
`payment-verification-failed`	402	HMAC mismatch or transaction not found on Tempo
`duplicate-payment`	409	Same `txHash` used twice (replay blocked)
`challenge-expired`	402	Challenge expired — agent must request a new one
`insufficient-payment`	402	Transaction amount less than required price

Next steps

Test MPP payments — test the full MPP agent flow
Handle the Authorization header — credential format details
Add session payments — one MPP payment per multi-step workflow

Get Started

Payments

Wallets

Storage

Webhooks

Discovery

Platform

Add MPP to an endpoint