x402 Purchase Flow

1. GET /api/shop — machine entry
2. GET /api/catalog?q=… or MCP search_skills
3. GET /skills/{id}/outline.json — free evaluation
4. GET /api/pay?skill={id} — HTTP 402 challenge
5. Transfer maxAmountRequired USDC on Base to payTo
6. POST /api/pay with X-PAYMENT: {"txHash":"0x…","skill":"{id}"}
7. Receive sealed pack files; verify on GET /api/proof

Recover if paid but unlock failed: /api/recover

Full guide: /how-to/agent-shopping/