{
  "schema_version": "lvl-knowledge-lesson-v1",
  "id": "path-ae-03-x402-in-five-steps",
  "category": "path",
  "path_ids": [
    "understand-agent-economy"
  ],
  "title": "x402 in five steps (conceptually)",
  "summary": "HTTP 402 Payment Required as a commercial protocol: challenge, settle, unlock — without monthly seats.",
  "body": "## What x402 is\n\n**x402** revives HTTP status **402 Payment Required** for machine payments. The server says: *this resource costs X; pay here; then retry with proof.*\n\n## Five steps (no wallet required to understand)\n\n1. **Discover** a skill id in the catalog  \n2. **Evaluate** free outline / sample  \n3. **Challenge** — `GET` pay endpoint returns 402 with `maxAmountRequired`, `payTo`, network, asset  \n4. **Settle** — transfer exact USDC (atomic units) on Base to `payTo`  \n5. **Unlock** — `POST` with payment proof (`txHash` + skill); receive sealed files  \n\n## Why exact amount matters\n\nIf the transfer is short by one micro-unit, verification fails. Agents must copy `maxAmountRequired` from the challenge, not guess from a UI label.\n\n## Re-redeem\n\nA verified `txHash` is an entitlement key: the same payment can re-download the pack without paying twice (idempotent redeem).\n\n## Takeaway\n\nx402 is a challenge-response payment loop over ordinary HTTP — designed for agents first, usable by humans too.",
  "concepts": [
    "x402",
    "402-challenge",
    "base-usdc",
    "idempotent-redeem"
  ],
  "related_skills_optional": [
    {
      "skill_id": "agent-x402-first-buy",
      "name": "Agent x402 First Buy",
      "price_usd": 0.05,
      "price_label": "$0.05 / unlock",
      "summary": "$0.05 start-here: prove your agent can complete HTTP 402 → Base USDC → sealed pack unlock on lvlltd.com.",
      "outline": "https://lvlltd.com/skills/agent-x402-first-buy/outline.json",
      "challenge": "https://lvlltd.com/api/pay?skill=agent-x402-first-buy",
      "listing": "https://lvlltd.com/listings/agent-x402-first-buy/",
      "available": true,
      "optional": true,
      "label": "optional_implementation"
    }
  ],
  "sort_order": 30,
  "estimated_minutes": 10,
  "last_updated": "2026-07-22T12:00:00.000Z",
  "freshness": {
    "last_updated_at": "2026-07-22T12:00:00.000Z",
    "days_since_update": 0,
    "band": "fresh",
    "score_0_100": 95,
    "label": "Fresh",
    "display": "Fresh · updated 2026-07-22 (0d ago)"
  },
  "integrity": {
    "knowledge_free": true,
    "skills_optional": true,
    "note": "This lesson is complete without purchasing any skill."
  },
  "related_bundles_optional": [],
  "url": "https://lvlltd.com/learn/lessons/path-ae-03-x402-in-five-steps/",
  "updated_at": "2026-07-22T21:10:40.587Z"
}