--- title: "Step 4: A settled round trip on both rails" step: 4 status: published updated: 2026-09-10 description: "Two x402 payments the house already made — one in USDC on Base, one in USDC on Solana — written out step by step with timestamps, amounts and full transaction hashes, and what each step does and does not prove." --- Plenty of writing explains how x402 works. Very little of it shows a settled payment end to end — the unpaid request, the 402 challenge, the signed authorization, the facilitator's verify and settle, the receipt on chain — with times you can check against a public ledger. This page is two of ours, one per rail. Nothing was bought to write it: both round trips settled days before the page existed, in the ordinary course of putting two endpoints live, and every figure comes from a house record or a keyless read of the public chain. **Both are house-to-house payments.** In each case the buyer wallet and the receiving address are ours, and both buyers are listed as house payers in the sellers' own config — [Step 2](/guides/payments/house-traffic-tagging/) is that convention. They prove the rails settle. They prove nothing about demand. ## Prerequisite on Solana: the payTo's USDC account must exist first A Solana token balance lives in an associated token account (ATA) owned by the wallet, and the account for a mint must exist before anyone can send that token to it. **The CDP facilitator does not create a missing destination ATA**, so a Solana route whose payTo has never held USDC cannot be paid at all. The house learned this by hitting it, before the settlement in Round trip B: 1. A payment went to a payTo with no USDC ATA. CDP's verify answered **HTTP 400** with `preflight_validation_failed`, and **nothing moved** — on the `exact` scheme for Solana no funds change hands until the facilitator submits, so a failed preflight leaves no artefact on chain. 2. The ATA was created once, owner-funded, at about **0.00204 SOL** rent. 3. The identical call then settled. The same refusal appeared on another house property on **2026-09-02 at 04:57Z** and cleared the same way. If you sell on Solana, create the payTo's USDC account before you advertise the rail. *(House record on the first Solana settlement, 2026-09-01; house build log, 2026-09-02.)* ## Round trip A — USDC on Base **parallax402.com `GET /v1/window`, 10000 atomic USDC ($0.01), settled 2026-09-02.** An owner-approved drill against a route that had just gone live. **1. Unpaid request → 402.** A `GET` with no payment header returns the terms: in the JSON body for x402 v1, and base64 in the `PAYMENT-REQUIRED` response header for v2. The v1 entry for this route: ```json { "scheme": "exact", "network": "base", "maxAmountRequired": "10000", "resource": "https://parallax402.com/v1/window?from=&to=", "payTo": "0x790fE337b89900028E16fE63Cc087112F7a2BA49", "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "maxTimeoutSeconds": 60, "extra": { "name": "USD Coin", "version": "2" } } ``` *Proves:* price, asset and destination are stated before anything is signed, and `resource` names what the money is for. *Does not prove:* that the endpoint will answer. A query naming a window and getting it wrong is a `400` with nothing settled — a malformed-query probe returned exactly that on both rails. **2. The buyer signs an authorization.** On the `exact` scheme for an EVM chain the buyer signs an EIP-3009 authorization for exactly the amount and destination in that envelope. It signs; it does not send, and it pays no gas. *Proves:* consent to one amount and one recipient. *Does not prove:* that anything happened. An authorization nobody submits simply goes unused. **3. The seller asks the facilitator to verify.** The payload and the same requirements object go to CDP's `verify`. A verdict can arrive on a 4xx as well as a 200 — read the body, not the status. *Proves:* the signature covers these exact terms and the buyer can pay. *Does not prove:* that money moved. Verify is a check, not a transfer. **4. Settle, then serve.** parallax builds the fact from its own store before settling — a window it holds no census for is a `404` with nothing charged — and releases the answer only once the transfer lands. | Field | Value | |---|---| | Transaction | `0x12f31243ae1b27077c8f350c379af10f69df7db16c0fd8f0957218f8d3479071` | | Block | 50,766,699 | | Block time | 2026-09-02T04:19:05Z | | Amount | `10000` atomic USDC — $0.01 | | From | `0x632ff2f904cc6ab6d741a42014c4c483f328e92f` (house buyer) | | To | `0x790fE337b89900028E16fE63Cc087112F7a2BA49` (payTo) | | Status | success | Read for this page on 2026-09-10 with two keyless JSON-RPC calls against `https://mainnet.base.org`, and readable by anyone at . The receipt carries an authorization-used log and the ERC-20 `Transfer` of `10000` to the payTo, and the account that submitted it and paid the gas — `0x42dd53906b49c202e8e934b059dc019e04634b00` — is not the buyer. *Proves:* the amount, both addresses, the block, the time, and that the facilitator relays. *Does not prove:* who controls either address, or that value came back the other way. **5. The ledger row.** The seller wrote the settlement to its own ledger with `house=1`, because the payer is on its `HOUSE_PAYERS` list. *Proves:* verify, settle, ledger and tagging all ran. *Does not prove:* revenue — the flag exists so this row is excluded from any revenue number. The house task record for this route opened at **2026-09-02T03:52:46Z** and closed at **04:23:46Z**; the block time falls inside that window. ## Round trip B — USDC on Solana **toolshed.lemon-agent.dev `/convert/json-yaml`, 2000 atomic USDC ($0.002), settled 2026-09-01T05:20:40Z.** The house's first settled Solana payment, and where the prerequisite above was learned. **1. Unpaid request → 402.** The offer carries a Solana entry beside the Base one: scheme `exact`, network `solana` in v1 (CAIP-2 `solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp` in v2), amount `2000`, asset the USDC mint `EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v`, payTo `7zXRc8sYkhjezbwXQw43beBrKDmhTMA7mkNfqRjdZ6gw`, and — the field Base does not have — `extra.feePayer`, the account that pays the network fee. It is **drawn from a rotating facilitator pool, not a constant**: read it per protocol version rather than pin it. The registry's copy of this route's Solana entry, in a full catalogue walk on 2026-09-05, names `D6ZhtNQ5nT9ZnTHUbqXZsTx5MH2rPFiBBggX4hY1WePM`; that walk found 20 distinct feePayer values across the catalogue. *Proves:* price and destination are stated up front here too. *Does not prove:* that the payTo can receive — which is what the first attempt discovered. **2. The buyer signs a transaction.** Not an EIP-3009 authorization: on Solana the buyer signs a transaction the facilitator's feePayer will co-sign and submit. *Proves:* consent to one transfer. *Does not prove:* that it is admissible. Simulation happens later, at the facilitator. **3. Verify.** CDP verified the payload against the same requirements the 402 advertised. Ledger `verify_ok=1`. *Proves:* the payload matched the advertised terms. *Does not prove:* settlement — the failed first attempt stopped here. **4. Serve, then settle.** The toolshed chassis is ordered the other way round from parallax: the caller gets the conversion, and the settlement runs after the response. A conversion is cheap and re-derivable; a paid *fact* is not, which is why parallax withholds until the transfer lands. Ledger `settle_ok=1`. *Proves:* the ordering is a deliberate choice, not an accident. *Does not prove:* that either order is right for your product. **5. The receipt.** | Field | Value | |---|---| | Signature | `4C4EMmWv7dFA679fhfGXV9rC4K3veqLYJVgJ2UqfYUojH1RN1y3xUhpLt5HeGX7aiP7CCGPjRxpW4NTyKAhUThLN` | | Slot | 443,342,687 | | Block time | 2026-09-01T05:20:40Z | | Buyer USDC account | `CosTwK5g9kw5URsUtT725BYoYfC5nYKiT6ZceRDfWeKq`, 5.000000 → 4.998000 | | Recipient account | 0.000000 → 0.002000, freshly created | | Amount | `2000` atomic USDC — $0.002 | Those figures come from the house record's own chain read of **2026-09-04** against `https://api.mainnet-beta.solana.com`. The read attempted for this page on 2026-09-10 was rate-limited by that public endpoint and not retried, so the slot and block time here are the record's rather than a fresh confirmation; the transaction is public at . That earlier read also corroborated the failed first attempt the only way a chain can corroborate a non-event: the buyer account's whole history contains no errored transaction. ## What these two receipts prove, and what they do not They prove that both rails settle end to end on the same chassis against the same facilitator; the amount, asset, payer and payee of each transfer at a named block and time, checkable without an account or a key; that the order of operations is observable, and that a seller chooses where "serve" sits in it; and that on Solana the ATA precondition is a hard gate whose failure mode is a verify-time refusal rather than a lost payment. They do not prove: - **Demand.** Both are house-to-house; no third party is involved. - **That the buyer got value.** A receipt records a transfer, not whether the response was worth $0.01. - **Anything about facilitator fees.** These receipts name none; the house build log for 2026-09-02 records no settlement fee observed on that day's on-chain receipts, a separate observation from these two transactions. - **That the endpoints still behave this way.** Prices, routes and chassis change; the chain records those two days. If you sell over x402, the cheapest honest thing you can publish is one settlement in full, with the parts you cannot vouch for marked as such. ## Sources Internal records have no public URL and are named rather than linked. - **House record, first Solana settlement, 2026-09-01** — signature, slot, block time, balances, the `preflight_validation_failed` first attempt, ATA rent, the rotating feePayer pool, and the 2026-09-04 chain read confirming them. - **House campaign ledger, E18, 2026-09-02** — the Base drill: verify, settle, transaction hash, `house=1`, the malformed-query probe. - **House task record for the route, 2026-09-02** — the drill's open and close times, 03:52:46Z and 04:23:46Z. - **House build log, 2026-09-01 and 2026-09-02** — the estate-wide Solana proving run, the second ATA refusal at 04:57Z, the no-settlement-fee observation. - **Registry catalogue walk, 2026-09-05** — the Solana offer entry for `/convert/json-yaml`, and 20 distinct feePayer values. - **Public chain, read 2026-09-10** — Base block number, block time, transfer amount, both addresses, the submitting account, status. Truncated hashes in the internal records are omitted here rather than shown in part: a receipt you cannot look up is not a receipt.