Blog

Engineering notes from building 402s.shop. x402 protocol, payment rails, agent-callable APIs.

May 2, 2026

Agents can now buy 402s.shop credits autonomously (verified end-to-end with real USDC)

New endpoint: POST /api/buy-credits/{small|medium|large} — agent signs an EIP-3009 USDC transfer for the package amount, server settles on Base mainnet, returns a fresh API key with credits. Verified end-to-end with $1 USDC on Base mainnet today. Plus the key-as-auth dashboard pattern (no signup ever).

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May 2, 2026

Two silent footguns shipping x402 to Base mainnet (and a 4-endpoint crypto cluster)

I shipped 402s.shop's x402 mainnet rail and a four-endpoint crypto cluster on the same Saturday. The mainnet path took two non-obvious bug fixes (different facilitator URL with JWT auth, different EIP-712 domain name) that the testnet path silently glossed over. Notes for anyone building on x402.

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