Settled x402 payments but not listed in the Bazaar? Your client is not echoing extensions

The symptom

Everything looked right: 13 tools returning spec-perfect 402 responses with a valid extensions.bazaar block (verified against the JSON Schema), 14 payments settled on Base mainnet through the CDP facilitator, on-chain transactions confirmed. Yet 14+ hours later:

GET https://api.cdp.coinbase.com/platform/v2/x402/discovery/merchant?payTo=0x4395...
{"pagination": {"total": 0}, "resources": []}

The investigation

The CDP "Get discovered" docs contain two crucial details that are easy to miss:

• The x402 spec says clients must echo the server's extensions in the PaymentPayload: "Servers advertise supported extensions in PaymentRequired, and clients echo them in PaymentPayload." This echo is how your discovery metadata physically reaches the facilitator — it rides inside the payment, through /verify and /settle.
• The facilitator answers /verify and /settle with an EXTENSION-RESPONSES header (base64 JSON) carrying the bazaar cataloging status: success, processing, or rejected with a reason.

Our test buyer built its payment payload with resource, accepted and the signature — but no extensions. So every payment settled perfectly, and the facilitator never received a byte of listing metadata. And because we never read EXTENSION-RESPONSES, the absence was invisible.

The fix (one line in the client, one habit in the server)

// buyer: echo the 402's extensions verbatim
const paymentPayload = {
  x402Version: 2,
  resource: required.resource,
  accepted: req,
  payload: { signature, authorization },
  ...(required.extensions ? { extensions: required.extensions } : {}),
};

// seller: decode the facilitator's verdict on every settle — never fly blind again
$header = $response->header('EXTENSION-RESPONSES');
$status = $header ? json_decode(base64_decode($header), true) : null;
// {"bazaar": {"status": "processing"}}  → accepted, cataloging asynchronously
// {"bazaar": {"status": "rejected", "rejectedReason": "..."}} → fix and repay

Minutes after re-sending one payment per tool with the echo in place, every settle returned {"bazaar": {"status": "processing"}} — and the merchant discovery endpoint went from total: 0 to total: 13 within the next indexing cycle.

Takeaways

• Settlement success ≠ discovery success. They travel together but are validated separately.
• If you build your own x402 client, echo extensions — official SDKs do it for you; hand-rolled buyers forget it.
• Log EXTENSION-RESPONSES on every settle. It is the only place the facilitator tells you why your listing is (not) happening.
• Expect up to ~6 hours for ranking/search updates — the Bazaar recalculates on a cycle, so verify with the merchant endpoint, not search.