Developer shares field guide for migrating live x402 payment APIs from V1 to V2

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A developer running x402ai, a payment-gated API settling real USDC on Base mainnet, has published a practical migration guide for moving x402 services from V1 to V2. The migration is not forced by crashes but by two pressures: V1 services are rejected by the x402scan discovery tool used by autonomous agents, and V2-capable clients silently fail when hitting V1 middleware, generating unexplained invalid_payload errors in server logs. Key breaking changes include a package namespace shift from the frozen x402-hono to the scoped @x402/* family, the challenge moving from the response body to a base64-encoded header, and network identifiers switching to CAIP-2 format such as eip155:8453. The guide also flags that TLS-terminated proxies must explicitly set resource URLs to https://, as the X-Forwarded-Proto header is no longer respected in V2. All code samples in the guide are verified against @x402/* 2.19.0 and @coinbase/x402 2.1.0 running in production as of July 2026.

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