Pay for hosting over the Machine Payments Protocol.

MPP on Tempo, the evm method, and a card

MPP (the Machine Payments Protocol, backed by Stripe and Tempo) defines several ways to pay: an on-chain Tempo method that settles on Tempo, an evm method that settles on chains like Base, and a Stripe card method. Stacktree settles the Tempo method on Tempo (USDC.e) and the evm method on Base, the same on-chain rail our x402 support runs on. Both are proven with real settlements on mainnet. Since 20 October 2026, /publish and /provision also take the stripe method: a card or Link, as a Stripe Shared Payment Token, answering the method="stripe" challenge in the same 402. An agent pays with whatever it holds.

The fastest way to pay is the multi-rail front-door at agents.stacktr.ee/api/publish: POST your HTML, get a 402, pay $0.50 over MPP (Tempo) or x402 (USDC on Base or Solana), and the page publishes to a private link, no key needed. See MPP in production for the on-chain receipt.

How an agent pays

The agent calls POST /provision with no credentials and gets a 402. The challenge is a standard MPP Payment header:

WWW-Authenticate: Payment id="..." realm="api.stacktr.ee"
  method="evm" intent="charge" expires="..." request="<base64url>"

The request decodes to the amount, the USDC contract on Base, and the recipient. An MPP client signs the EIP-3009 authorization and retries. With mppx, that is a few lines of config and one call:

// mppx.config.js
import { defineConfig } from 'mppx/cli'
import { evm, assets } from 'mppx/evm/client'
import { privateKeyToAccount } from 'viem/accounts'

export default defineConfig({
  methods: [...evm({ account: privateKeyToAccount(process.env.PRIVATE_KEY), assets: [assets.base.USDC] })],
})

mppx https://api.stacktr.ee/provision -X POST   # funded Base wallet, ~$1 USDC

The client signs, the facilitator settles, and the response carries a stk_live_ key. Use it as a normal bearer token to publish.

It works, with real money

This is not a sandbox. An mppx client paid exactly $1.00 USDC on Base mainnet over the evm method, with the facilitator covering gas, and the key it received published a page that is still up. The settlement is on-chain and anyone can verify it: the transferWithAuthorization on BaseScan, a $1.00 USDC transfer from the paying wallet to Stacktree, no human in the loop.

MPP and x402, one rail underneath

MPP's evm method and x402 are two discovery and challenge formats over the same money movement: the agent signs an EIP-3009 USDC authorization and a facilitator settles it on Base. Stacktree speaks both on the same /provision endpoint, so an agent carrying either client can pay. That is the point. You should not have to pick the protocol your hosting accepts before you know which one your agent speaks. After provisioning, the same à-la-carte unlocks apply: make a site permanent, add a custom domain, or raise limits, each paid the same way. The catalogue is at GET /unlock and the accepted rails at GET /provision.

What is live, honestly

MPP over the evm method is live on Base mainnet today, settling real USDC through the Coinbase CDP facilitator, and it is listed for discovery on MPPScan and submitted to the mpp.dev registry. The Tempo method is live at the agents.stacktr.ee front-door. The stripe method (a card or Link as a Shared Payment Token) is live on /publish and /provision since 20 October 2026. How many payments each rail has taken, zero included, is counted live in the agent record.