Two records, side by side
An agent hits a paid endpoint and two different records can come back. They look similar and prove completely different things. Here they are, both live.
The payment record: a live Day Pass 402 challenge
Fetched from the live endpoint on October 24, 2026. Fetch it yourself any time: curl https://zambo.dev/api/x402/day-pass returns HTTP 402 with this challenge:
{
"x402Version": 2,
"error": "Payment required",
"accepted": {
"scheme": "exact",
"network": "eip155:8453",
"asset": "0x833589fcd6edb6e08f4c7c32d4f71b54bda02913",
"amount": "990000",
"payTo": "0xb753be5Eac5B29c711051DfF91279834e9C9b9AC",
"maxTimeoutSeconds": 900
},
"resource": "https://zambo.dev/api/x402/day-pass"
}What it proves: that $0.99 in USDC on Base was asked for, and once the signed payment settles, that the payment happened. Settlement is a fact about money.
The work record: an AER-1 receipt of a tool call
A real receipt from a call an agent ran after connecting: a live BTC price check, saved the moment it executed.
Receipt: https://zambo.dev/run/26b353a9-8e34-4820-a351-9a65208e11c1
Check it free, no account: zambo.dev/verify, or offline with the npm verifier or aer1-verify for Python.
What it proves: which tool ran, what it was given, and the exact saved result, committed under a sha-256 digest at execution time, so the record was not changed afterward.
Why the difference matters
A payment receipt answers "did the money move?" It cannot answer "did the agent do the work, and what did it actually return?" An agent can pay for access and then do nothing, do the wrong job, or report a result it never got, and the payment record looks identical in all three cases. The work receipt is the record of the work itself: an agent receipt is a record of one ai agent tool call that anyone can check: it keeps the exact saved bytes and their sha-256 digest, and it proves the result was not changed since it was saved, not that it was right. When the job is later disputed, the payment record settles the bill. The work receipt settles the argument.
How the two fit together on Zambo
An agent pays the Day Pass over x402 with no human in the loop: one payment of $0.99 USDC on Base opens 24 hours of the Zambo MCP endpoint. From the first call after activation, every call returns an AER-1 receipt at a public link, including calls that are rejected. Payment opens the door; receipts cover everything that happens inside.
Prices, exactly: Day Pass $0.99 for 24 hours. Zambo Pass $29 for 30 days, one payment; $290 for 365 days; $19 for 30 days for $ZAMBO holders. Both passes give identical access. Humans pay by PayPal or card through PayPal at zambo.dev/add; agents pay with USDC on Base via x402.
Frequently asked questions
Does an x402 payment receipt prove the work was done?
No. An x402 payment record proves settlement: that the amount asked for was paid. It says nothing about what the agent did afterward. The record of the work is a separate thing: an AER-1 receipt of the tool call itself, which shows the tool, the inputs, and the exact saved result.
What does the Zambo Day Pass 402 challenge contain?
The live challenge at zambo.dev/api/x402/day-pass is an x402 version 2 challenge: scheme exact, network eip155:8453 (Base), the USDC asset address, amount 990000 (which is $0.99), the payTo address, and a 900 second timeout. Pay it and the Day Pass activates for 24 hours.
How much does the Day Pass cost?
The Day Pass is $0.99 for 24 hours, one payment, paid by agents in USDC on Base via x402 or by humans with PayPal or card through PayPal. The Zambo Pass is $29 for 30 days, one payment, or $290 for 365 days, and $19 for 30 days for $ZAMBO holders. Both passes give identical access.
What is an agent receipt?
An agent receipt is a record of one ai agent tool call that anyone can check: it keeps the exact saved bytes and their sha-256 digest, and it proves the result was not changed since it was saved, not that it was right.
Can an agent pay and start working with no human involved?
Yes. The Day Pass is designed for exactly that: an agent reads the 402 challenge, signs the payment with its wallet, retries the call, and is activated for 24 hours. Every call it then makes returns a verifiable receipt at a public link, so a human can check the work afterward without having been present.