> ## Documentation Index
> Fetch the complete documentation index at: https://docs.algovoi.co.uk/llms.txt
> Use this file to discover all available pages before exploring further.

# Agentic Payment Receipts

> Verifiable agentic payment receipts across x402, AP2, A2A and MPP. Offline recomputable, no PII, on one shared JCS (RFC 8785) canonicalisation substrate.

Every agentic payment protocol answers *how an AI agent pays*. None of them, on their own, answer
*how you prove (years later, offline, to a supervisor) that the payment was screened, authorised, and
settled correctly*. That proof is the **receipt layer**, and it is where AlgoVoi sits across the whole
ecosystem.

AlgoVoi issues **deterministic, recomputable, offline-verifiable receipts** for **x402, AP2, A2A and
MPP**, all anchored on one shared [JCS canonicalisation substrate](/canonicalisation-substrate) so
that a receipt emitted under any protocol re-verifies byte for byte at year N, independent of AlgoVoi.

## Why a receipt layer, across all four protocols

The agentic-payments ecosystem is converging on four protocols: [x402](/protocols/x402),
[AP2](/protocols/ap2), [A2A](/protocols/a2a) and [MPP](/protocols/mpp). They differ in *how* an agent
is charged (per request, per mandate, per agent-call, per method) but share one unmet requirement:
**a portable, verifiable record of the compliance and settlement decision** that outlives the session
that produced it.

A receipt layer is valuable only if it holds three properties:

* **Deterministic.** The same logical decision serialises to the same bytes everywhere. AlgoVoi pins
  [JCS, RFC 8785](/canonicalisation-substrate) as the canonical preimage form.
* **Recomputable.** Anyone can re-derive the hash from the retained bytes, with no dependence on an
  out-of-band rule registry, via an in-band `canon_version`.
* **Offline-verifiable and no PII.** Verification needs no live call to AlgoVoi, and the receipt
  carries categorical outcomes, not customer data. See the [compliance receipt format](/compliance-receipt)
  and [receipt verifier](/receipt-verifier).

## One substrate, every protocol

| Protocol                | What it charges for                  | AlgoVoi receipt                                                  |
| ----------------------- | ------------------------------------ | ---------------------------------------------------------------- |
| [x402](/protocols/x402) | per HTTP request (`HTTP 402`)        | compliance receipt at admission, settlement attestation on-chain |
| [AP2](/protocols/ap2)   | per signed mandate                   | mandate-bound compliance receipt plus settlement attestation     |
| [A2A](/protocols/a2a)   | per agent-to-agent task              | payment-gated task receipt on the same substrate                 |
| [MPP](/protocols/mpp)   | per JSON-RPC method or MCP tool call | per-method compliance receipt                                    |

All four resolve to the same receipt grammar over the same canonical bytes. The
[`action_ref`](/canonicalisation-substrate) primitive,
`SHA-256( JCS( { agent_id, action_type, scope, timestamp_ms } ) )`, binds the agent, the action, and
the settlement into one recomputable anchor regardless of which protocol carried the payment.

## How a receipt is proven

1. The gateway screens the incoming request (sanctions / PEP / AML, bring-your-own provider) and
   emits a categorical **ALLOW / REFER / DENY** [compliance receipt](/compliance-receipt).
2. The receipt is canonicalised under [JCS RFC 8785](/canonicalisation-substrate) and signed
   (RFC 9421, with a post-quantum option via the [PQC substrate](/pqc-substrate)).
3. On settlement, a [settlement attestation](/retention-chain-substrate) chains the on-chain
   transaction to the same `action_ref`.
4. Any party recomputes the canonical bytes and verifies the signature **offline**, at any later
   date, with the open [receipt verifier](/receipt-verifier).

## Standards backing

The substrate is specified in AlgoVoi-authored IETF Internet-Drafts and cross-validated **byte for
byte across eight independent JCS implementations in eight languages**:

* [`draft-hopley-x402-canonicalisation-jcs-v1`](https://datatracker.ietf.org/doc/draft-hopley-x402-canonicalisation-jcs-v1/): the canonicalisation discipline.
* [`draft-hopley-x402-compliance-receipt`](https://www.ietf.org/archive/id/draft-hopley-x402-compliance-receipt-00.html): the compliance receipt format.

See [authorship and provenance](/substrate-authorship-provenance) and the
[x402 document index](/x402-document-index) for the full record.

## Next

* Start with the [JCS canonicalisation substrate](/canonicalisation-substrate).
* See the per-protocol pages: [x402](/protocols/x402), [AP2](/protocols/ap2),
  [A2A](/protocols/a2a), [MPP](/protocols/mpp).
* Verify a receipt yourself with the open [receipt verifier](/receipt-verifier).
* [Verifiable x402 receipts](/verifiable-x402-receipt) — the complete x402 receipt chain explained.
* [Offline-verifiable agent receipts](/offline-verifiable-receipts) — proven offline across eight independent implementations.
* [No-PII compliance receipts](/no-pii-compliance-receipt) — screening verdict with no wallet address in the canonical bytes.