> ## 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.

# Verifiable x402 Receipts

> Issue and verify x402 payment receipts. AlgoVoi pins JCS (RFC 8785) and SHA-256 so any party recomputes a verifiable x402 receipt offline, no account needed.

An x402 payment proves that a transfer happened on chain. A **verifiable x402 receipt** proves what the chain does not record: that a compliance screen ran at admission, that settlement reached a stated state under a named party's risk model, and that the record has not been altered since it was issued. AlgoVoi issues that receipt on every x402 request and pins it to a canonicalisation discipline so anyone can verify it byte for byte.

## What makes an x402 receipt verifiable

The receipt is a JSON object canonicalised under [RFC 8785 (JCS)](https://www.rfc-editor.org/rfc/rfc8785) and hashed with SHA-256. The hash is content-addressed: it is a deterministic function of the receipt fields, so a verifier who holds the receipt recomputes the same hash and confirms the bytes independently. No issuer call, no registry lookup, no AlgoVoi service. A JSON parser, JCS, and SHA-256 are the entire dependency.

Because the canonicalisation rule is pinned in-band as `canon_version: jcs-rfc8785-v1`, the receipt re-verifies under the exact rules it was issued under, years later, without an out-of-band registry.

## The receipts AlgoVoi issues on x402

| Receipt                                           | Records                                   | Closed enumeration                          | Issued on                                            |
| ------------------------------------------------- | ----------------------------------------- | ------------------------------------------- | ---------------------------------------------------- |
| [Compliance receipt](/compliance-receipt)         | The admission-time screening decision     | `ALLOW` / `REFER` / `DENY`                  | `POST /checkout/{token}`                             |
| [Settlement attestation](/settlement-attestation) | The settlement state on a given chain     | `SETTLED` / `PENDING_FINALITY` / `REVERSED` | `POST /checkout/{token}/verify`, `POST /x402/verify` |
| [Refund receipt](/refund-receipt)                 | The refund outcome, chained to settlement | `FULL` / `PARTIAL` / `REJECTED`             | refund flow                                          |

Each receipt chains to the previous one by `content_hash`, so a verifier walks admission, then settlement, then refund under one byte-deterministic pin. Every value is a positive, byte-distinct record: a `DENY` receipt is not missing data, it is a verifiable artefact in its own right.

## Verify one yourself

The hosted verifier confirms a content-addressed reference with no auth:

```bash theme={null}
POST https://verify.algovoi.co.uk/action-ref
Content-Type: application/json

{ "agent_id": "did:web:api.algovoi.co.uk", "action_type": "payment.authorize",
  "scope": "base:0x2d96f2bc", "timestamp_ms": 1748534400000 }
```

Or reproduce the full corpus offline, with hand-written JCS and stdlib SHA-256, so the published values are proven without AlgoVoi's canonicalizer being invoked at all:

```bash theme={null}
git clone https://github.com/chopmob-cloud/algovoi-jcs-conformance-vectors
cd algovoi-jcs-conformance-vectors
pip install algovoi-substrate
python composition/verify_corpus.py
python composition/first_principles_check.py
```

The construction is cross-validated across eight independent JCS implementations in eight languages at 880/880 cumulative agreements, including the RFC 8785 author's own Java implementation. When eight implementations that share no code produce the same bytes, the result is a property of the standard, not of any one library.

## Specification and authorship

The receipts and the canonicalisation discipline they pin are AlgoVoi-authored and specified in IETF Internet-Drafts:

* [`draft-hopley-x402-canonicalisation-jcs-v1`](https://datatracker.ietf.org/doc/draft-hopley-x402-canonicalisation-jcs-v1/) — the JCS discipline (`urn:x402:canonicalisation:jcs-rfc8785-v1`)
* [`draft-hopley-x402-compliance-receipt`](https://datatracker.ietf.org/doc/draft-hopley-x402-compliance-receipt/) — the admission receipt
* [`draft-hopley-x402-settlement-attestation`](https://datatracker.ietf.org/doc/draft-hopley-x402-settlement-attestation/) — the settlement attestation

Reference implementations are published Apache-2.0: [`algovoi-substrate`](https://pypi.org/project/algovoi-substrate/) (Python) and [`@algovoi/substrate`](https://www.npmjs.com/package/@algovoi/substrate) (TypeScript), byte-for-byte identical on the same input.

## See also

* [Offline-verifiable agent receipts](/offline-verifiable-receipts) — verify with no service call
* [No-PII compliance receipts](/no-pii-compliance-receipt) — screening evidence with no personal data
* [Verify it yourself](/verify-it-yourself) — reproduce every vector offline
* [Canonicalisation substrate](/canonicalisation-substrate) — the JCS discipline
* [Substrate authorship and provenance](/substrate-authorship-provenance) — citable AlgoVoi authorship record