Pay for hosting over the Machine Payments Protocol.

MPP over the evm method

MPP (the Machine Payments Protocol, backed by Stripe and Tempo) defines several ways to pay: an on-chain evm method, a Tempo method, and a Stripe card method. Stacktree implements the evm method, settling USDC on Base mainnet through an x402 facilitator. That is a deliberate choice, not a limitation: the evm method needs only a wallet, so it works for any agent and in any region, and it is the same on-chain rail our x402 support already runs on. We do not advertise the Tempo or Stripe methods, because we do not settle them, and a discovery hint an agent acts on should be one that actually pays.

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 not implemented. The Stripe (Shared Payment Token) method is US-only and gated until that suite reaches our region. We would rather ship one method that genuinely settles than three that mostly do not.