x402 Premium ACP Feed - Droplinked Developers

The standard ACP product feed is open and free — every catalog item Droplinked exposes to agentic shoppers lives there. The endpoint at /feed/acp.premium.json is gated by the x402 HTTP 402 micropayment protocol, and it is Droplinked’s working reference implementation of that protocol on Base mainnet.

Read this before you pay for it. The x402 gate is real and fully functional — the challenge, the signature verification, and the settlement all work, and this page documents them accurately. The premium payload behind the gate is not populated yet: the handler currently returns {"items": [], "next_cursor": null, "generated_at": "…", "premium": true}. Use this endpoint to build and test an x402 client against a live mainnet gate. Do not build a data dependency on its body — for catalog data use the free ACP feed or the MCP server, both of which return real inventory today.

Like /feed/acp.json, this is a JSON API, not an ACP-ingestible file. The ACP file spec accepts tab- or comma-delimited .tsv, .txt, or .csv and rejects JSON — so an ACP ingester cannot read the premium endpoint either. Use it from your own code, and submit the delimited artifact (https://droplinked-public-feeds.s3.amazonaws.com/acp/latest.tsv.gz) to ingesters. There is no x402-gated delimited artifact today. Background: Feed formats.

The price is intentionally per-call rather than per-subscription so an autonomous agent can pull the feed on demand without operating a Droplinked subscription.

At a glance


Endpoint	`GET https://apiv3.droplinked.com/feed/acp.premium.json`
Protocol	x402 — `402 Payment Required` per call
Settlement	USDC on Base mainnet
Price per call	$0.001 (1,000 atomic USDC units, 6 decimals)
Facilitator	Coinbase CDP facilitator — the only path that settles on Base mainnet. The public `x402.org` facilitator is unauthenticated and testnet-only; it is not what production uses.
PayTo	Returned live in the challenge (Droplinked treasury). Read it from the response, don’t hard-code it.
Settlement primitive	EIP-3009 `transferWithAuthorization`
Asset	`0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913` (Circle USDC on Base)

The protocol in three round-trips

1. Agent: GET /feed/acp.premium.json                       (no payment)
   Droplinked: 402 Payment Required
   Body: {
     "scheme":   "exact",
     "network":  "base",
     "maxAmountRequired": "1000",
     "asset":    "0x833589f…",
     "payTo":    "0xB2721aD7…",
     "resource": "https://apiv3.droplinked.com/feed/acp.premium.json",
     "mimeType": "application/json",
     "extra":    { "name": "USD Coin", "version": "2", "currency": "USDC" }
   }
   (the same challenge is mirrored base64-encoded in the `X-Payment-Required` header)

2. Agent (off-protocol): signs a USDC transfer for 1,000 atomic units to `payTo`
                          on Base mainnet, gets back a payment proof.

3. Agent: GET /feed/acp.premium.json
          Header: X-PAYMENT: <serialised proof>
   Droplinked: facilitator verifies proof → 200 OK + JSON feed body

The first call always returns 402 — there is no API key authentication. Every authorised caller is identified by a signed payment proof. extra.name and extra.version are the EIP-712 domain the transfer authorisation must be signed over. Sign against the domain the challenge gives you (name: "USD Coin", version: "2") — a signature produced over any other domain will not verify, and a plain USDC transfer that skips the authorisation entirely is not a payment proof. Fetch the live challenge:

curl -sS https://apiv3.droplinked.com/feed/acp.premium.json | jq .

How agents typically integrate this

Most agent SDKs that target Coinbase / Anthropic / OpenAI surfaces ship with x402 support out of the box. The pattern is:

The agent has a CDP (Coinbase Developer Platform) wallet or another EIP-1559 wallet with USDC on Base.
The wallet is configured with a per-request signing budget (e.g. “spend up to $1 USDC per minute on x402-gated endpoints”).
The agent’s HTTP client transparently retries the second-round GET with the X-PAYMENT header when it sees a 402, using cached proofs to avoid re-signing within a quote window.

If you’re building an agent without SDK support, you can implement the full handshake by reading the x402 protocol spec.

What’s in the premium feed

The response shape is compatible with /feed/acp.json, so an agent that already consumes the open JSON endpoint can point at this one without changing its parser:

{ "items": [], "next_cursor": null, "generated_at": "2026-09-20T23:38:18.897Z", "premium": true }

items is currently empty. The premium projection — the extra per-row signals and the uncapped pagination described in the endpoint’s OpenAPI summary — is not wired up yet. The gate ships ahead of the payload deliberately, so that agent developers have a live mainnet x402 endpoint to integrate against while the data side is built. When the payload lands, this page will state exactly which fields it carries. Until then, assume none.

The request budget still applies. The 402 challenge itself is returned with x-ratelimit-limit: 60 — paying per call does not exempt a caller from the global rate limit. See Rate limits.

Failure modes

HTTP status	Reason
`402`	First call — present a signed payment proof in `X-PAYMENT` and retry.
`503` `X402_NOT_CONFIGURED`	Operator has not set `X402_FACILITATOR_URL`. Surface to operator, do not retry.
`503` `X402_FACILITATOR_UNAVAILABLE`	Facilitator circuit breaker is OPEN. Retry with exponential backoff.
`4xx` after `X-PAYMENT`	Payment proof rejected — re-sign with a fresh nonce.
`200 OK`	Body is the premium feed JSON.

Why x402 (and not API keys)

x402 was chosen over API keys for the same reason Droplinked is built on EAS attestations: the buyer/agent identity is the cryptographic signature, not a long-lived shared secret held by an account team. There’s no key to rotate, no key to leak, no quota to provision. An agent operator pays for the calls they actually make, settles in USDC on-chain, and gets no recurring bill. The trade-off is that agent wallets need USDC on Base ($0.001 per call is trivial but non-zero), and the protocol is younger than HTTP Basic. Both gaps are being closed by the broader x402 ecosystem — Storyflo’s premium-briefing MCP tool uses the same facilitator and settlement pattern as a reference integration.

ACP product feed — the open, unauthenticated version, including the delimited artifacts an ACP ingester can actually read
Storefront MCP discovery — tool-level discovery for agents that don’t want to ingest a bulk feed
Merchant Discovery Rules — how KYB verification gates merchant visibility (which in turn drives premium-feed ranking)
x402 protocol — external protocol spec

​At a glance

​The protocol in three round-trips

​How agents typically integrate this

​What’s in the premium feed

​Failure modes

​Why x402 (and not API keys)

​Related

At a glance

The protocol in three round-trips

How agents typically integrate this

What’s in the premium feed

Failure modes

Why x402 (and not API keys)

Related