Agentic payments (x402) - Droplinked Developers

Droplinked settles agent payments in USDC on Base mainnet using x402, Coinbase’s HTTP 402 Payment Required micropayment protocol. The gate is live on production: you can see a real challenge right now, without credentials. USDC-on-Base is not an arbitrary pick. TRM Labs reports that 99.6% of settled x402 value is USDC, so a single asset on a single chain covers effectively the whole protocol’s volume — which is why Droplinked supports exactly that and does not ask an agent to hold anything else.

See it working

curl -i https://apiv3.droplinked.com/feed/acp.premium.json

HTTP/2 402
x-payment-required: <base64 of the JSON body below>

{
  "scheme": "exact",
  "network": "base",
  "maxAmountRequired": "1000",
  "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  "payTo": "0x…",
  "resource": "https://apiv3.droplinked.com/feed/acp.premium.json",
  "description": "droplinked premium ACP product feed — per-call micro-payment",
  "mimeType": "application/json",
  "outputSchema": {},
  "extra": { "name": "USD Coin", "version": "2", "currency": "USDC" }
}

Field	Value
Network	Base mainnet
Asset	`0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913` — Circle’s USDC on Base
Scheme	`exact`
Amount	`1000` atomic units — USDC has 6 decimals, so $0.001
Settlement primitive	EIP-3009 `transferWithAuthorization`, verified through the Coinbase CDP facilitator

payTo is returned live in the challenge — read it from the response rather than hard-coding it.

Signing correctly

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"). Two failure modes that look like bugs and are not:

A signature produced over a different domain will not verify.
A plain USDC transfer that skips the authorisation is not a payment proof. x402 needs the signed authorisation, not the transfer.

Then re-request with the serialised proof in the X-PAYMENT header.

What an agent can do today

Discover and read inventory — free, no credentials

Droplinked runs a public MCP server. Read tools are open; no key, no account.

Surface	Tools
`https://mcp.droplinked.com/mcp` (streamable HTTP, stateless)	38 tools — merchant and inventory discovery, trust-fabric verification, cart composition, lending
`https://apiv3.droplinked.com/mcp/v1`	11 read tools including `searchProducts`, `findInventory`, `getProductDetail`, `getShopInfo`, `listMerchants`, `searchMerchants`, `getMerchantDirectory`, `getMerchantCatalogSummary`, `getInventoryHealth`, `getStockoutAlerts`

Manifest: https://mcp.droplinked.com/.well-known/mcp.json. Send Accept: application/json, text/event-stream on JSON-RPC calls. Write tools require X-MCP-API-Key when the server is key-gated.

curl -sS -X POST https://apiv3.droplinked.com/mcp/v1/tools/call \
  -H 'content-type: application/json' \
  -d '{"name":"searchProducts","arguments":{"query":"shirt","limit":2}}'

That returns real production catalog rows.

Pay an x402-gated resource

The premium feed endpoint above is a working reference implementation of the full handshake. See x402 Premium ACP Feed — including what its payload does and does not contain today.

Order-level x402 routes

These are mounted and authenticated. They are the checkout-side rails, and they are the part of the stack most likely to change, so confirm current behaviour with us before you build against them:

Route	Caller
`POST /v2/orders/:orderId/x402-pay`	The owning buyer or merchant. Returns `402` with the payment descriptor when `X-PAYMENT` is absent; settles and confirms the order when it is present and valid.
`POST /v2/agentic/orders/:orderId/x402-settle`	A consumer agent. The agent analogue of the route above. The signed payment binds to this path, so a proof minted for `/x402-pay` will not verify here — the resource in the challenge is the path you must sign for.

Platform metering

Route	Purpose
`POST /platform-billing/x402/quote`	Quote a metered platform call
`POST /platform-billing/x402/settle`	Settle it
`GET /platform-billing/x402/credits`	Read remaining credits
`GET /platform-billing/metered/ping`	Metering reachability check

Limits you should know before you design around this

A merchant cannot currently be paid in USDC. x402 settles to the platform. There is no merchant-owned x402 payout destination configured today, so there is no merchant settlement leg to route to. Treat x402 on Droplinked as a platform and agent-surface payment rail, not as a merchant payout rail. Anything describing turnkey stablecoin settlement for merchants is roadmap.

Rate limits still apply to 402 responses. The premium feed carries x-ratelimit-limit: 60 like any other endpoint — paying per call does not exempt you from the request budget. See Rate limits.
Base mainnet only. No testnet path is published, so there is no free way to exercise the full handshake end to end. Budget real (if tiny) USDC for integration testing.

Failure modes

Response	Meaning	What to do
`402`	First call, or an invalid/absent proof. Body is the descriptor.	Sign and retry with `X-PAYMENT`.
`503` `X402_NOT_CONFIGURED`	No facilitator configured on this environment.	Surface to the operator. Do not retry.
`503` `X402_FACILITATOR_UNAVAILABLE`	Facilitator unreachable or its circuit breaker is open.	Exponential backoff.
`400` `X402_ORDER_NOT_CONFIRMABLE`	Order is not in a payable state.	Do not retry; re-read the order.
`400` `X402_SETTLE_FAILED`	Facilitator rejected settlement; reason appended.	Re-sign with a fresh nonce.

​See it working

​Signing correctly

​What an agent can do today

​Discover and read inventory — free, no credentials

​Pay an x402-gated resource

​Order-level x402 routes

​Platform metering

​Limits you should know before you design around this

​Failure modes

​Related

See it working

Signing correctly

What an agent can do today

Discover and read inventory — free, no credentials

Pay an x402-gated resource

Order-level x402 routes

Platform metering

Limits you should know before you design around this

Failure modes

Related