x402 Receipt Verifier

Gold402 Verified. Hand-reviewed and on the curated list — curation is the bar. The stamp means a human read this entry and the endpoint answered when we knocked. It is not a delivery test: we have not paid this service and graded what came back, so treat it as "reachable and speaks the protocol," never as "this is worth the money."

Audits NEXUS's own x402 payment logs against its own delivery logs and issues a signed HMAC receipt proving a specific payment correlates with a real, successful delivery; signature-only verification is free. $0.02 USDC on Base Sepolia (testnet) via x402 on the 2 paid routes. Example: `POST /verify-payment-receipt {"asset_name":"document-conversion-api","payer_address":"0x0000000000000000000000000000000000dEaD","claimed_amount_usd":0.01,"claimed_at":"2026-08-24T00:00:00Z"}`. ([OpenAPI](https://x402-receipt-verifier-325572559480.us-central1.run.app/openapi.json)) ([Agent Card](https://x402-receipt-verifier-325572559480.us-central1.run.app/.well-known/agent-card.json)) ([GitHub](https://github.com/nexus-mcp-infra/x402-receipt-verifier))