Pay per request with MPP

You can pay for a Particle API request with USDC on Base using the Machine Payments Protocol. MPP uses the same per-call prices and payable endpoints as x402. You do not need an account or an API key.

Choose a protocol

When MPP is available, the same 402 Payment Required response advertises both payment options. Read the challenge returned by the endpoint to discover its current price and accepted method.

	x402	MPP
Challenge	`PAYMENT-REQUIRED`	`WWW-Authenticate: Payment ...`
Payment	`PAYMENT-SIGNATURE`	`Authorization: Payment ...`
Receipt	`PAYMENT-RESPONSE`	`Payment-Receipt`
Payment method	`exact`, USDC on Base	`evm`, `charge`, USDC on Base

Send exactly one payment credential per request. A request containing both an x402 payment and an MPP payment receives 400 before either is verified.

Pay with an MPP client

Use an MPP client with the EVM charge method and a wallet holding USDC on Base. A client configured only for Tempo cannot pay a Base challenge.

npm install mppx viem

import { Fetch, evm } from "mppx/client";
import { privateKeyToAccount } from "viem/accounts";

const fetch = Fetch.from({
  acceptPaymentPolicy: { origins: ["https://api.particle.pro"] },
  methods: [evm.charge({
    account: privateKeyToAccount(process.env.WALLET_PRIVATE_KEY as `0x${string}`),
    currencies: [evm.assets.base.USDC],
    maxAmount: "1.00",
  })],
});

const response = await fetch(
  "https://api.particle.pro/v1/podcasts/search?q=artificial%20intelligence",
);
console.log(response.status, response.headers.get("Payment-Receipt"));
console.log(await response.json());

The client reads the challenge, signs the requested USDC transfer, and retries with Authorization: Payment .... Set maxAmount to your per-request budget.

Prices and retries

The MPP challenge’s encoded request contains the amount in atomic USDC units, the token address, recipient, and chain ID. USDC has six decimal places: 25000 means $0.025. Use the quoted amount instead of hard-coding a price. A challenge expires after five minutes and applies to the exact method, path, query string, and request body. If you change the request, obtain a new challenge. Successful payments return a Payment-Receipt with the transaction reference. Failed API requests and MCP tool errors are not charged. If settlement times out, retry the identical request with the same payment credential first: the transfer might have completed even if the response did not arrive. Authorize a new payment only after an explicit rejection.

API keys and MCP

API keys and account Bearer credentials keep their existing behavior and take precedence over per-request payments, including when a key is invalid. For MPP, omit account credentials and send only the Authorization: Payment credential. MPP is also available over HTTP on POST https://mcp.particle.pro/mcp. The price is the sum of the request’s billable tool calls. initialize, tools/list, ping, and free tools remain free. An unpaid tool call advertises both payment protocols and the OAuth Bearer challenge so your client can choose how to connect. Alerts, account endpoints, and other endpoints that require an account retain their existing restrictions. See what can be paid for.

Agent discovery

MPP uses OpenAPI discovery. Agents and registries can read the public documents without authentication:

REST discovery lists the API operations.
MCP discovery, available when MPP is enabled, describes the HTTP MCP endpoint.
The agent map lists endpoints and tools with their per-call prices. The setup playbook explains how to connect.

The OpenAPI root’s x-service-info supplies service categories and documentation links. Payable operations include x-payment-info.offers[] with method: "evm", intent: "charge", the USDC token address, and an amount in atomic units. MCP uses amount: null because its total depends on the requested tools. Both documents describe the Payment authentication scheme and payment headers. Discovery is advisory: use the runtime 402 challenge for the current terms. MPP offers are advertised only when enabled. MPP discovery uses /openapi.json; the existing /.well-known/x402 documents continue to describe x402. You can check either document with the reference validator:

npx mppx discover validate https://api.particle.pro/openapi.json

Getting started

Recipes

Podcasts

Companies

Knowledge graph

Alerts

Errors

Pay per request with MPP

Choose a protocol

Pay with an MPP client

Prices and retries

API keys and MCP

Agent discovery

​Choose a protocol

​Pay with an MPP client

​Prices and retries

​API keys and MCP

​Agent discovery

​Related

Choose a protocol

Pay with an MPP client

Prices and retries

API keys and MCP

Agent discovery

Related