How to prove to a client that AI did the work you billed for

When a client pays for AI agent work, they are buying something they cannot see. A line item that says "agent ran 400 tool calls" is your word against their skepticism. The fix: attach a verifiable receipt to every billed line item, so the client verifies the work themselves with one click. The receipt format is AER-1, defined in IETF Internet-Draft draft-zambo-aer1.

See it working: run one free call and get a real verifiable receipt, no signup.

See it live: generate a real verifiable receipt in 30 seconds, no signup.

The freelancer and agency trust problem

Selling AI agent work creates a dispute neither side can resolve with words:

  • The client cannot inspect the work. Hours on a timesheet are legible. Hundreds of agent tool calls are not. The deliverable may be excellent, but the client has no window into what actually ran.
  • Screenshots are not proof. Anyone can screenshot a terminal. An export of a chat log can be edited before sending. The client knows this, even if they never say it.
  • Disputes default to discount. When a client questions the work and you have no evidence, the conversation ends with you cutting the invoice. Evidence ends that conversation before it starts.

What the client really wants is not a longer report. It is something they can check themselves, without taking your word for it.

The fix: receipts as invoice attachments

For each billed session or task, mint an AER-1 receipt per tool call (or one chained receipt bundle for the whole run), and attach it to the invoice:

  1. Run the work with receipt collection on. Every tool execution gets a receipt: identifier, creation time, tool and caller scope, the exact bytes of the result, and a SHA-256 output commitment. Receipts chain together, so the whole run is one verifiable record.
  2. Reference the receipts on the invoice. Next to each line item, cite the receipt identifiers or the bundle: "Website research pass: 214 tool calls, receipt bundle 9f3a...". The invoice now points at evidence, not just a number.
  3. Include the verification link. One link, zambo.dev/verify, where the client pastes a receipt or clicks through the bundle. No account, no signup, no software to install.

The client does not need to understand the cryptography. They see "verified" on the receipt they checked, for the work you billed. That is the whole proof, and it runs in seconds.

The verification link the client can click

What the client experiences

They open zambo.dev/verify, paste the receipt from your invoice, and get a verdict: the stored result matches what the tool returned, or it was tampered with. They never needed your account, your platform, or your word. The checker is public and the format is an open IETF Internet-Draft, so anyone can implement their own verifier and get the same answer.

That independence is the point. Evidence the client checks themselves ends disputes. Evidence only you can produce starts them.

What to send with the invoice

Make it a repeatable packet, the same shape every time:

  • The invoice PDF with receipt identifiers cited per line item.
  • The receipt bundle (JSON), one file per billed session, hash-chained per run.
  • The verification link (zambo.dev/verify) printed on the invoice, next to the receipt references.
  • Your own archive copy. Keep the same bundle you sent. If a dispute ever reaches anyone else's desk, you both hold identical evidence.

Clients who receive this twice start expecting it. It becomes your differentiator: the freelancer whose invoices come with proof.

What receipts prove, and what they do not

Say it plainly to the client, because honesty is what makes the proof credible: a verifiable receipt proves the saved record was not changed. It proves the tool ran and the result is exactly what the tool returned. It does not prove the answer was correct, that the right tool was chosen, or that the outcome was worth the price. Quality is still your reputation. The receipt just removes the argument about whether the work happened.

Mint your first proof-of-work receipt now

Generate a real verifiable receipt on the try page in 30 seconds, no signup. Verify it at zambo.dev/verify, then read the format behind it: draft-zambo-aer1 on the IETF Datatracker. Your next invoice can carry proof.

Proving AI work to a client: FAQ

How do I prove to a client that my AI agent did the work?

Attach the receipts to the invoice. Run the work with receipt collection on, and each step lands as a verifiable receipt at a public URL. Send the client the receipt links, or one handover link for the whole job: they open it, check the steps, and Accept or Flag. They need no account and none of your tooling.

My client refuses to pay because an AI did the work. What proof do I send?

Send the handover link for the job: the goal, every step with its receipt, the sources each step checked, and the acceptance state. A client who can check the work itself is arguing about the work, not about whether an AI touched it. The dispute kit page covers the refusal case step by step.

Can my client check the receipts without my account?

Yes. Verification is public: anyone holding a receipt link can open the verify page, paste the receipt, and recompute the commitment. The format is the open AER-1 Internet-Draft, so an independent verifier gets the same answer yours does.

Related

Browse the public registry of AER-1 implementations.

See it on a real call: the live demo runs one real Zambo call and hands you its verifiable receipt, no signup. To put a receipt under every call your agent makes, a Zambo Day Pass unlocks everything for 24 hours for $0.99.