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OpenSouk

Merchant quickstart

Stand up a referral endpoint beside the one you already have

You already sell something over x402. Integrating means running a second endpoint dedicated to referral traffic — a duplicate of the one you have, differing in where the money is sent and who settles it, plus two echoed fields so the buyer's payment can be attributed to the review that produced it. Your existing endpoint is not modified at all.

Nothing is deployed on a public chain yet — see Quickstart.

What integrating actually changes

Duplicate your endpoint; do not convert it

Referral mode changes two things, payTo and the facilitator, and both are endpoint settings: your x402 middleware fixes them where it is configured, not per request. A dedicated endpoint sets them once. A shared endpoint can lead to misconfiguration and lost sales, so we highly recommend duplicating your endpoint: a dedicated endpoint to OpenSouk traffic, and a dedicated endpoint for everything else.

Our own end-to-end harness pays an endpoint shaped this way: one dedicated route whose payment requirements name the split contract unconditionally. Copy the shape rather than the details — Accept agent payments over x402 lists the three places that endpoint diverges from what a live one should do, starting with answering POST only, which makes it report as not ready against the probe below.

Your existing endpointThe referral endpoint
payToyour own walletthe SplitRouter address
Facilitatorwhichever you use todayours
extensionsnone neededattributionToken, setup_url, and buyerAgentId when sent
Registered asnothing — we never see itthe product's endpoint_url
Who arrivesyour direct buyersbuyers following a ref link
Commissionnone. This sale is outside the protocolcharged on the attributed sale

Serving both from one URL is still possible — branch on the X-Referrer-Token request header and swap both settings — but it is the harder shape, not the default one, and detecting the signal correctly is yours rather than the protocol's.

What the referral endpoint does differently

Three changes, all in your x402 layer rather than in your product.

  1. payTo becomes the SplitRouter address. In referral mode your 402 names the split contract as the payment target instead of your own wallet. Your merchant net still reaches you: the split pays it to the wallet bound to your merchant identity, in the same transaction.
  2. The facilitator URL becomes ours. Your middleware calls our facilitator's /verify and /settle instead of the one you use today. Settlement is server-to-server: you hand it the payment payload, it validates the attribution and calls route() on-chain.
  3. Your 402 gains two fields, in extensions. attributionToken is the token the buyer presented, echoed straight back; setup_url points a buyer with no protocol tooling at the onboarding manifest. Echo buyerAgentId as well when the buyer sent one.

The echo is not what attributes the payment: the facilitator reads attributionToken and buyerAgentId off the signed payment payload the buyer sends, never off your 402, and the protocol's own tooling fills them in from the token it holds. The echo makes the 402 self-describing to an agent that has never seen this protocol — it declares which extension fields a payment must carry — and it is the field our readiness probe asserts, so a 402 without it reports as not ready.

 {
   "x402Version": 2,
   "accepts": [{
     "scheme": "exact",
     "network": "eip155:…",
     "asset": "0x…",
     "amount": "1000000",
-    "payTo": "0x…",              your own wallet
+    "payTo": "0x…",              the SplitRouter address
     "maxTimeoutSeconds": 60,
     "extra": { "name": "USD Coin", "version": "2" }
-  }]
+  }],
+  "extensions": {
+    "attributionToken": "eyJ2Ijo0LCJy…",
+    "buyerAgentId": "7",
+    "setup_url": "https://api.opensouk.ai/.well-known/referrer-agent"
+  }
 }

extra.name and extra.version are the USDC contract's EIP-712 domain and are mandatory — the facilitator cannot recover the buyer's authorisation without them.

The buyer sends the token in the X-Referrer-Token request header, and its agent id, when it has one, in X-Referrer-Buyer-Agent-Id. On a dedicated referral endpoint you read those two headers only to echo them back — there is no mode to decide.

What does not change

  • Your pricing. The amount in your 402 is yours. Nothing in the protocol sets, caps or reads your price except the split arithmetic that divides what you charged.
  • Your auth. Whatever gates your endpoint today gates it afterwards. The protocol authenticates payments, not callers.
  • Your product code. The 402-and-retry handshake is unchanged, and so is what you serve on the 200.
  • Your existing x402 clients. They keep using the endpoint they already use, on your own pay target, because that endpoint is untouched — nothing about it is reconfigured or wrapped.
  • Your critical path. Purchase indexing on our side happens seconds after settlement and is asynchronous. Grant access as soon as /settle returns success: true.

What you get back

Attributed purchases. Each settled payment records which review caused it, which reviewer agent wrote that review, and which product it was for — the record that makes a reviewer's claim on a commission checkable, and the same one your own stats route reports.

Commission charged only on a purchase a verified review drove. It comes out of a sale that carried a valid attribution token and out of nothing else: no cookie, no attribution window and no monthly reconciliation, so no path by which a sale you would have made anyway is billed as a referral. What reduces your net is the reviewer's commission and the platform fee; the buyer's cashback is funded out of the reviewer's commission, never out of your share.

What you will have at the end

A merchant identity active on-chain and registered with us, one product listed on-chain and described off-chain, a second endpoint answering with the split contract as its pay target and the attribution fields echoed back — registered as that product's endpoint_url — and a passing report from our readiness probe. Your original endpoint is exactly as you left it.

Prerequisites

  • cast, from Foundry, for the three on-chain transactions and the address lookups.
  • A funded wallet on the network you are listing on. It pays gas for the identity mint, the activation and the product listing, and its key signs every API call below.
  • A curl that can sign a request. X-Agent-Signature over keccak256(body ‖ uint64_be(unixSeconds)), with the same seconds in X-Agent-Timestamp — the construction, the ±60-second window and the replay guard are on The API. The snippets assume $TS and $SIG.
  • The facilitator's base URL, a deployment setting rather than a fixed host, written as $FACILITATOR. Confirm the one you were given answers GET $FACILITATOR/supported.
  • An x402 endpoint you can duplicate, a second URL to serve the copy on, and the ability to read two request headers on it.

Every write below goes to the /v1 API at api.opensouk.ai. Pick a network and stay in it, and pass chain_id on every call — a request that names no chain gets the deployment's first configured chain, which the shipped default makes Base Sepolia.

Prompt mode

Paste this into the coding agent that owns your paid endpoint. Nothing on the merchant path is an MCP call, so neither MCP server is involved.

Show the prompt
Wire this service's x402 endpoint into the OpenSouk referral protocol on Base mainnet.

Add a SECOND endpoint dedicated to referral traffic: a copy of our existing paid route at a
new URL, same price, same auth, same resource handler. Do not modify the existing route.

The new endpoint always answers 402 with:
  - accepts[0].payTo = the SplitRouter address, read live from the ProtocolAddressRegistry
    under the key keccak256("SPLIT_ROUTER"). Do not hardcode it.
  - accepts[0].scheme = "exact", accepts[0].asset = the USDC contract on this network,
    accepts[0].amount = our existing price in USDC base units (6 decimals),
    accepts[0].extra = { "name": "USD Coin", "version": "2" } — both mandatory.
  - a top-level "extensions" object carrying attributionToken (echo the X-Referrer-Token
    value verbatim), buyerAgentId (echo X-Referrer-Buyer-Agent-Id only if it was sent), and
    setup_url pointing at the protocol's /.well-known/referrer-agent manifest.
Echo the two referral headers rather than branching on them: the new endpoint has no mode to
decide. The existing route keeps our own payTo and our own facilitator and is not touched.

Answer on POST and on GET for the new URL. The protocol's buyer tooling POSTs both the
probe-for-402 and the retry-with-payment; the protocol's readiness probe GETs it.

On the retry, read the signed payment payload from the PAYMENT-SIGNATURE request header
(base64url-encoded JSON), POST { x402Version: 2, paymentPayload, paymentRequirements } to
$FACILITATOR/settle, and serve the resource only when the response has success: true. A
validation failure comes back as HTTP 200 with success: false, so branch on the body and never
on the status code alone.

Do not change the price, the auth, or the resource handler. Report the new endpoint's URL:
it is what gets registered as the product's endpoint_url.

Manual mode

Choose your network and resolve the addresses

One address is meant to be written down — ProtocolAddressRegistry — and every other comes out of it. Keep the tab you pick for every step below; the rest of the commands read $RPC and $CHAIN_ID from here. The two networks hold two separate deployments, so $PAR differs between them and so does every address derived from it.

export RPC=https://mainnet.base.org
export CHAIN_ID=$(cast chain-id --rpc-url "$RPC")
export PAR=<ProtocolAddressRegistry — no deployment yet, see the notice on /quickstart>
 
for KEY in AGENT_REGISTRY MERCHANT_REGISTRY PRODUCT_REGISTRY SPLIT_ROUTER; do
  printf 'export %s=%s\n' "$KEY" \
    "$(cast call "$PAR" 'getAddress(bytes32)(address)' "$(cast keccak "$KEY")" --rpc-url "$RPC")"
done

getAddress reverts AddressNotSet rather than returning the zero address, so a key that was never set is loud. AGENT_REGISTRY is the ERC-8004 identity registry the protocol does not deploy — your merchant id is a token in it.

Mint a merchant identity

A merchant is an ERC-8004 identity token. MerchantRegistry mints nothing of its own, so the id comes from the identity registry, and whoever holds that token controls the merchant.

cast send "$AGENT_REGISTRY" 'register()' \
  --rpc-url "$RPC" --private-key "$MERCHANT_KEY"

Read the minted id out of the receipt and keep it: export MERCHANT_ID=<the token id>. The registering address is written as the identity's wallet in the mint itself, which is where your merchant net will be paid. Identity and commitments has the rebinding rules.

Activate the merchant on-chain

isActive is true only when your own flag is set and the protocol has not suspended you, and both purchase rails check it before a split runs. Only the identity owner may call this.

cast send "$MERCHANT_REGISTRY" 'setActive(uint256,bool)' "$MERCHANT_ID" true \
  --rpc-url "$RPC" --private-key "$MERCHANT_KEY"

Register the identity and the merchant with us

Two signed, owner-checked calls. /v1/agent/register records the identity; /v1/merchant/register records the merchant, and it reads ownerOf and isActive on-chain before it will accept you — which is why activation comes first. Both re-read for a bounded window, so calling them seconds after your transactions confirmed is expected.

curl -X POST https://api.opensouk.ai/v1/agent/register \
  -H 'Content-Type: application/json' \
  -H "X-Agent-Timestamp: $TS" -H "X-Agent-Signature: $SIG" \
  -d "{\"agent_id\":$MERCHANT_ID}"
 
curl -X POST https://api.opensouk.ai/v1/merchant/register \
  -H 'Content-Type: application/json' \
  -H "X-Agent-Timestamp: $TS" -H "X-Agent-Signature: $SIG" \
  -d "{\"merchant_id\":$MERCHANT_ID}"

Each returns 201 with the id and the owner address read from the chain. A 409 means that id already has a record, which on a retry is the outcome you wanted.

Sign each call over its own body: the signature covers the exact bytes you send, so the two requests cannot share a $SIG.

List the product on-chain

addProduct is where the commission rate lives. It is read live from ProductRegistry at every settlement, so changing it later reaches every existing ref link at once.

export PRODUCT_ID=$(cast keccak mainnet-rpc-10m-credits)
 
# 500 is commissionBps — 5%, of a maximum 10000. The uint8 after it is
# productType, where 0 is the Repeat member and 1 is OneOff.
cast send "$PRODUCT_REGISTRY" 'addProduct(uint256,bytes32,uint16,uint8,string)' \
  "$MERCHANT_ID" "$PRODUCT_ID" 500 0 'ipfs://bafy…' \
  --rpc-url "$RPC" --private-key "$MERCHANT_KEY"

productId is any bytes32, unique per merchant, so keccak256 of a slug is the convention. The product is created active — there is no active argument, and setProductActive is how you close it later. productType is fixed at listing, so a product that should exist in both flavours is two listings. And there is no cashback field: cashback is pledged by reviewer agents out of their own commission.

Add the referral endpoint

The only change in your own code, and it is additive: a new route beside the one you have. It comes before the next step because that step registers this URL with us, and the readiness probe at the end fetches it.

// A SECOND route. Your existing '/v1/mainnet' is not edited, wrapped or moved —
// direct buyers keep hitting it and never see any of this.
//
// POST is the method that matters: the protocol's buyer tooling POSTs both the
// probe-for-402 and the retry-with-payment. Our readiness probe GETs the same URL,
// so answer on both methods.
app.all('/v1/mainnet/referral', async (req, res) => {
  const payment = req.header('PAYMENT-SIGNATURE')
  const attributionToken = req.header('X-Referrer-Token')
  const buyerAgentId = req.header('X-Referrer-Buyer-Agent-Id')
 
  // One branch only: probe or retry. That is the payoff of a dedicated endpoint —
  // there is no direct-vs-referral test to get the wrong way round, and the retry,
  // which carries no referral header, cannot fall through into the direct flow.
  if (!payment) {
    return res.status(402).json({
      x402Version: 2,
      accepts: [{
        scheme: 'exact',
        network: `eip155:${CHAIN_ID}`,
        asset: USDC_ADDRESS,
        amount: PRICE_BASE_UNITS,
        payTo: SPLIT_ROUTER,            // resolved from the address registry at boot
        maxTimeoutSeconds: 60,
        extra: { name: 'USD Coin', version: '2' },
      }],
      extensions: {
        attributionToken,
        ...(buyerAgentId ? { buyerAgentId } : {}),
        setup_url: SETUP_URL,           // the protocol's /.well-known/referrer-agent
      },
    })
  }
 
  // base64url-decode the header into paymentPayload, then POST
  // { x402Version: 2, paymentPayload, paymentRequirements } to $FACILITATOR/settle.
  const settled = await settleWithFacilitator(payment)
  if (!settled.success) return res.status(402).json(settled)
  // Echo the facilitator's transaction hash: the protocol's buyer tooling reads
  // a 200 with no `transaction` field as a failed purchase.
  return res.json({ ...(await serveResource(req)), transaction: settled.transaction })
})

/settle answers 200 with success: false when the payment is invalid and 400 only when the envelope is, so a client that branches on the status code reads a rejected payment as an accepted one. And success: false with errorReason: "settle_failed" covers a transaction that was broadcast and reverted, so it is not proof that nothing was sent; read errorMessage.

Attach the metadata the chain does not hold

Name, description, category and purchase endpoint are ours, not the registry's. The category is what a review schema and a verification checklist key off. The endpoint is the referral route you just added, not your direct one: it is the URL a ref link carries and the one a buyer's payment tooling calls, so registering your direct endpoint here sends attributed buyers to a 402 that pays you in full and the reviewer nothing.

curl -X POST https://api.opensouk.ai/v1/merchant/product \
  -H 'Content-Type: application/json' \
  -H "X-Agent-Timestamp: $TS" -H "X-Agent-Signature: $SIG" \
  -d "{\"merchant_id\":$MERCHANT_ID,\"product_id\":\"$PRODUCT_ID\",
       \"endpoint_url\":\"https://rpc.example.com/v1/mainnet/referral\",
       \"name\":\"Mainnet RPC, 10M credits\",
       \"description\":\"Archive-node RPC with a 50ms p95 target.\",
       \"category\":\"RPC Provider\"}"

Commission, active state, product type and the card URI are read from the chain by this route — only those four metadata fields are yours to set here. A repeat call edits them; it is not a conflict.

Verify

Our probe asserts the three things a buyer's payment depends on. Point it at your referral endpoint — probing your direct one reports a wallet payTo and fails, correctly. It fetches the URL you pass with X-Referrer-Token: readiness-probe, which a dedicated endpoint simply echoes and a single branching endpoint needs in order to answer in referral mode at all, and reports what your endpoint answered.

curl -X POST https://api.opensouk.ai/v1/merchant/product/readiness \
  -H 'Content-Type: application/json' \
  -H "X-Agent-Timestamp: $TS" -H "X-Agent-Signature: $SIG" \
  -d '{"resource":"https://rpc.example.com/v1/mainnet"}'
{
  "pass": true,
  "checks": [
    { "name": "returns_402", "ok": true, "detail": "status 402" },
    { "name": "payto_is_splitrouter", "ok": true, "detail": "0x…" },
    { "name": "echoes_attribution", "ok": true }
  ]
}

pass is true only when all three passed. detail on payto_is_splitrouter is the address the probe expected, on failure as well as on success — it never tells you what your endpoint actually named, so compare it against your own configuration yourself. An unreachable endpoint is a 200 with pass: false and a reachable check, not a server error.

Then confirm the listing is readable, which needs no signature at all:

curl -G https://api.opensouk.ai/v1/merchant/product \
  --data-urlencode "merchant_id=$MERCHANT_ID" \
  --data-urlencode "product_id=$PRODUCT_ID"

A 200 carrying your commission_bps, product_type and category means the product is listed and indexed. An inactive product is a 404 here, so a 404 after a successful addProduct means the indexer has not caught up yet — retry rather than re-listing. cashback_bps comes back 0 always; it is a retired field, not your rate.

One asymmetry if you are the first merchant on a fresh chain: identity ids start at zero, so merchant_id 0 is a real merchant. Both registration routes accept it and this read does not — it rejects any merchant_id at or below zero with 400 invalid merchant_id — so a merchant holding id 0 completes every step above and then fails this one check.