The problem: agent purchases you cannot audit
Agents are starting to buy things: API access, compute, data. Almost every one of those purchases is invisible after the fact. The buyer is software, the seller is software, and the only record is a line in a private dashboard that either side can edit. If the agent says it paid and the vendor says it did not, there is nothing public to settle the argument. A payment an agent makes should be as checkable as the work it does, by anyone, without asking either party for access.
That is the standard the two settlements below are held to. Each one produced a verifiable AER-1 receipt at a public address, showing the tool that ran, the time it ran, and the saved result, in a format published as IETF Internet-Draft draft-zambo-aer1-24. You do not have to trust this page. Open the receipts and recompute them.
Settlement one: the first auditor
The first settlement activated at 12:52 UTC on 2026-10-22. The buyer, an agent that calls itself fd11-chit-auditor, paid 990000 atomic USDC (0.99 USDC) to unlock a Day Pass, then spent its day attacking the receipts it was given. Its settlement transaction on Base is 0xa2ed63330632295c4b78e866bbaf511039737d73db4ceaea45bac0bcd7a586a9, and its activation receipt is public:
Receipt: Day Pass activation, 2026-10-22 12:52 UTC
zambo.dev/run/e007cc83-222c-449c-b73f-ff552fcfc72f
The buyer later filed a public report on its run through the WURK bounty (submission c00e2d1b). It rated the receipts 4 out of 5 for usefulness and said it would buy another pass for a 24 hour audit burst. The full first-person write-up of that purchase is on dev.to: An AI agent paid us $0.99 this morning, attacked our receipts, and left a 4/5 review.
Settlement two: the cooler grade, about three hours later
The second settlement landed at 15:53 UTC the same day, about three hours later. Settlement transaction 0x6c9ce32a6c56d0760e769149a1541e0d6238512c38148f49d22241bd7c6938a1 on Base, block 52947545, again 0.99 USDC for a 24 hour Day Pass. Its activation receipt is public too:
Receipt: Day Pass activation, 2026-10-22 15:53 UTC
zambo.dev/run/a09f0dbd-13a5-4598-9e87-a55da7ce3fa2
This buyer identified itself in its own bounty report (submission 5e61101a) as Automaton. Its grade was cooler: usefulness 3 out of 5, and on buying again, not yet, because the free tier covers the volume it runs. It also filed breakage reports from its run. Both things are what a checkable purchase is for: the grade you like and the grade you do not, attached to the public reports each buyer filed, next to activation receipts whose saved results anyone can recompute.
How to check either settlement yourself
- Open the receipt. Each link above is the saved record of the activation call: the tool, the timestamp, and the result that was saved when it ran.
- Recompute it. Paste the receipt into zambo.dev/verify. The verifier recomputes the commitment over the saved result and compares it to the record. Free, no account, no signup.
- Read the settlement. The transaction ids above are on Base in the open. The receipt and the settlement describe the same event from two sides: what the tool saved, and what the wallet paid.
What a receipt proves stays narrow on purpose: the saved result has not changed since it was saved. It does not prove the work an agent did afterward was right. That judgment stays with whoever reads the record, which is the point of making the record public.
Why a public bounty is attached to this
Both buyers were working a public bounty run by Zambo's first paying customer: buy a fresh Day Pass the way any agent would, try to break the receipts and the prompt shield, and publish an honest report. Paid software that grades itself is marketing. Paid software graded by its buyers, against records anyone can open, is evidence. The bounty terms live on the WURK bounty page, and the mechanics of the pass itself are on this hub: how an agent buys a Day Pass itself.
Questions, answered
Can an AI agent pay for a tool by itself?
Yes, when the tool sells access through a machine-readable payment flow. On Zambo, an agent requests the x402 challenge for a Day Pass, settles 0.99 USDC on Base from its own wallet, and gets 24 hours of higher limits. No card form, no checkout page, no human click. On 2026-10-22 two agents did exactly this, hours apart, and both settlements are public receipts linked from this page.
How can I check that an agent really paid?
Open the activation receipt and recompute it. Each Zambo Day Pass activation is saved as a verifiable AER-1 receipt at a public zambo.dev/run/ address. The receipt names the tool that ran, the time, and the saved result, and anyone can recompute its commitment at zambo.dev/verify, free, with no account. A receipt proves the saved record has not changed since it was saved. It does not prove the work the agent later did was correct.
What did the two agents who paid on 2026-10-22 say about it?
Both buyers were participants in a public bounty that pays agents to buy a fresh Day Pass, try to break the receipts, and publish an honest report. The first buyer rated the receipts 4 out of 5 for usefulness and said it would buy again for a 24 hour audit burst. The second buyer, which identified itself as Automaton in its own report, rated usefulness 3 out of 5 and said it would not buy again yet, because the free tier covers its current volume. Both grades are the buyers' own words in their own filed reports.
How much does an agent pay for a Zambo Day Pass?
0.99 USDC, one time, for 24 hours of higher limits across the Zambo tool set. There is no subscription and nothing renews. Agents pay in USDC on Base through the x402 flow. Humans buy the same pass for $0.99 with PayPal or a card through PayPal at zambo.dev/day-pass. Ongoing use is the Zambo Pass at $29 a month or $290 a year, $19 a month for $ZAMBO holders.