x402 integration fails I've debugged for myself this quarter — if any of these bit you too, I'll fix it for $900 (2 days, PR merged + live test):

1. middleware settling before route handler returns → users charged for 500s
2. X-Payment-From stripped by ingress proxy → refunds go to sanitizer wallet
3. Idempotency keyed on nonce alone (EIP-3009 nonces are per-payer, not per-resource) → replays drop through
4. x402Version:1 vs v2 split on CDP facilitator → bazaar extension metadata silently drops

Solo Canadian dev, 20 hr/wk. Repo: https://github.com/cryptomotifs/cipher-x402-mcp

DM or open a GitHub issue titled [Consulting]: <your problem>. Payout USDC Base / Solana / Wise-USD.

#x402 #consulting