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I built an MCP server where AI agents pay for their own compute in USDC

#ai #mcp #api #nanobanana

Agents can browse docs and call APIs, but they can't do checkout. No credit card form, no OAuth dance, no "verify your email". So when I shipped an AI generation API, the interesting question was: how does an agent pay?

What I built

An MCP server (https://livepairai.com/mcp, streamable HTTP) exposing ~70 image/video models behind one interface. An agent connects, lists models with prices, calls generate, and gets back either a result or an HTTP 402 with payment requirements.

The payment rail is x402 — USDC on Base. The flow:

POST /v1/agent/generate {model, prompt}
← 402 Payment Required

x-payment-requirements: {amount: "400000", currency: USDC, chain: base, payTo} → agent signs USDC transfer, retries with X-PAYMENT header ← 200 + result URL (hosted 48h, auto-deleted)

One HTTP round-trip pattern. No API key, no account, no session — the payment signature is the credential.

What actually happens inside

  • Model catalog with live per-call pricing: GET /v1/agent/models (5s 720p video ≈ $0.40, images ≈ $0.02–0.05)
  • Quote freshness was the annoying part — prices are per-result, so the 402 response carries a short-lived quote the agent must settle before expiry
  • For humans/API keys there's a chat-completions-compatible surface instead, so integrators who want accounting get Authorization: Bearer lp_… and skip the wallet dance entirely

Failure modes I hit

  • Agents that retry the original request without attaching payment — had to make the 402 body self-describing (amount, recipient, expiry, example header) so a generic agent could act on it without me hardcoding the client
  • Wallet-funded agents settling twice on timeout — made fulfillment idempotent on the payment reference
  • The privacy constraint shaped the storage layer: renders live 48h max, never indexed, share links are a separate opt-in path gated by model

Try it

  • MCP endpoint: https://livepairai.com/mcp
  • Agent docs: https://livepairai.com/SKILL.md
  • Manifest: https://livepairai.com/v1/agent/manifest.json

If your agent has a USDC wallet, it can already use this. Curious how others are handling

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