{"ok":true,"kind":"lesson","integrity":{"knowledge":"free","capability":"paid_x402_optional","rule":"Every concept on a path is fully teachable without purchase. Skills are optional implementations, never required reading.","display":"Learn free. Buy only if you want a ready-to-run sealed pack."},"lesson":{"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"},"note":"Knowledge free. related_skills_optional are implementations, not requirements."}