Internet-Draft x402-cancellation-receipt May 2026
Hopley Expires 1 December 2026 [Page]
Workgroup:
Independent Submission
Internet-Draft:
draft-hopley-x402-cancellation-receipt-01
Published:
Intended Status:
Informational
Expires:
Author:
C. Hopley
AlgoVoi

Categorical Mandate Cancellation Receipt Format for Agentic-Payment Flows

Abstract

This document specifies a categorical mandate cancellation receipt format for agentic-payment flows. The format records that a recurring-payment mandate or other standing payer-to-payee authorisation has been cancelled, by whom, for what reason, and with what effective date.

The receipt format uses a closed four-element enumeration of categorical outcomes (USER_REQUESTED, MERCHANT_REQUESTED, COMPLIANCE_TERMINATED, EXPIRED). The four-state enumeration preserves the regulatorily-load-bearing distinction between payer-initiated revocation, payee-initiated termination, operator/compliance-forced termination, and time-based expiry. A collapse to a three-state or binary representation loses operational distinctions that drive PSD2 (Directive 2015/2366) Article 64 refund-window obligations, Article 72 contractual-termination record-keeping, and POCA/AML evidence-chain linkage on compliance-forced terminations.

The format records two distinct timestamps -- when the cancellation was observed (cancellation_timestamp_ms) and when it takes legal effect (effective_from_ms) -- to support PSD2 Article 64(3)(a) direct-debit revocation timing, where the effective time is typically end-of-business-day prior to the next scheduled execution.

The format composes with the AlgoVoi-authored compliance receipt (draft-hopley-x402-compliance-receipt), settlement attestation (draft-hopley-x402-settlement-attestation), and refund receipt (draft-hopley-x402-refund-receipt) formats under the same canonicalisation discipline (draft-hopley-x402-canonicalisation-jcs). A verifier walking the audit chain confirms the full mandate lifecycle from admission through recurring execution to cancellation, and (where owed) onward to refund of revoked settled debits, under one byte-deterministic canonicalisation pin.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 1 December 2026.

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Table of Contents

1. Introduction

1.1. Motivation

Agentic-payment flows generate categorical receipts across the mandate lifecycle. Where the compliance receipt format (draft-hopley-x402-compliance-receipt) admits a mandate and the settlement attestation format (draft-hopley-x402-settlement-attestation) records recurring executions, mandate termination is the corresponding end-state. Termination is not a degenerate refund; it is its own state transition with its own regulatory consequences.

The operational and regulatory distinctions are load-bearing across four genuinely-different states:

  • A payer-initiated revocation (PSD2 (Directive 2015/2366) Article 64, UK Consumer Rights Act 2015 consumer-revocation provisions) MAY trigger refund obligations on debits already settled prior to the revocation effective date.
  • A payee-initiated termination (PSD2 Article 72 + contractual terms) records the end of a recurring billing arrangement but does NOT trigger consumer-revocation refund-window obligations on already-settled debits.
  • A compliance-forced termination (sanctions hit on payer, KYC failure, AML alert, court order, regulator directive) triggers POCA s.330 and AML 5+6 audit-chain evidence linkage back to the originating compliance event. The recorded receipt is the evidentiary anchor.
  • A time-based expiry (mandate reached its agreed end-date or maximum-execution count) records that the mandate's own terms terminated it. No party-initiated regulatory action is required beyond standard record-keeping.

A receipt format that collapses these to a three-state enumeration (e.g. PARTY_REQUESTED + AUTO_TERMINATED) loses the payer-vs-payee distinction that drives the PSD2 Article 64 refund-window obligation. A collapse to two-state (CANCELLED / EXPIRED) loses both that distinction and the compliance-forced flag that anchors the AML/POCA evidence chain.

This document specifies a cancellation receipt format that preserves the four-state categorical outcome at the canonical-bytes level and records the two timestamps (event recording time and legal effective time) independently.

1.2. Scope

This document specifies:

  • The canonical JSON shape of the cancellation receipt (Section 3).
  • The reference to the canonicalisation rule applicable to the receipt (Section 4 -- normative reference to draft-hopley-x402-canonicalisation-jcs, not redefined inline).
  • The audit chain composition under which cancellation receipts compose with compliance receipts, settlement attestations, and refund receipts (Section 5).
  • The year-N auditability properties the format pins (Section 6).
  • Composition patterns across the AlgoVoi receipt-format suite (Section 7).
  • Worked examples covering all four cancellation_reason outcomes (Appendix A).

This document does NOT specify:

  • The mandate format itself. The cancellation receipt references the mandate via a content-addressed mandate_ref of the form sha256:<hex>. The mandate record MAY be a compliance receipt, an Agent Payment Protocol (AP2) mandate object, a Merchant Payment Protocol (MPP) subscription record, or any operator-specific mandate format.
  • The refund flow triggered by a USER_REQUESTED cancellation. Refund obligations and their categorical receipt format are specified in draft-hopley-x402-refund-receipt. This document records only that the cancellation occurred and notes (per cancellation_reason) whether a refund obligation may apply.
  • The compliance event that drives a COMPLIANCE_TERMINATED outcome. That event is recorded in a separate compliance receipt (draft-hopley-x402-compliance-receipt) and linked via the audit chain.

1.3. Relationship to other Internet-Drafts

This document normatively references:

  • draft-hopley-x402-canonicalisation-jcs -- the JCS canonicalisation discipline pinned in Section 4.

This document is complementary to:

  • draft-hopley-x402-compliance-receipt -- admission-time compliance screening receipts. A cancellation receipt's mandate_ref MAY equal the content_hash of the compliance receipt that admitted the mandate.
  • draft-hopley-x402-settlement-attestation -- per-execution settlement attestations during the mandate's life.
  • draft-hopley-x402-refund-receipt -- post-cancellation refund receipts. A refund receipt's original_payment_ref MAY reference a settlement attestation that became refundable as a result of a USER_REQUESTED cancellation recorded under this document.

2. Conventions and Definitions

2.1. Notation

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

2.2. Definitions

cancellation receipt: a JSON object of the shape specified in Section 3, canonicalised under the discipline of draft-hopley-x402-canonicalisation-jcs.

content_hash: SHA-256, lowercase hex, of the JCS-canonical bytes of the cancellation receipt object.

mandate_ref: a string of the form sha256:<lowercase-hex-64> identifying the mandate record being cancelled by content hash. The mandate record itself is out of scope of this document.

cancellation_reason: a string-valued field carrying one of four closed enumeration values. See Section 3.1.

canon_version: an in-band string identifying the canonicalisation discipline. Fixed value jcs-rfc8785-v1 for this version.

3. Receipt Format Specification

A cancellation receipt is a JSON object with the following seven fields. All fields are REQUIRED. The receipt is canonicalised under draft-hopley-x402-canonicalisation-jcs per Section 4. Field names are sorted lexicographically by JCS during canonicalisation; the object itself uses arbitrary authoring order.

3.1. cancellation_reason

A string-valued field. The value MUST be one of:

  • USER_REQUESTED -- the payer revoked the mandate. PSD2 Article 64 applies. UK Consumer Rights Act 2015 consumer-revocation provisions apply. Triggers payer-side refund-window calculations for direct debits already settled prior to the effective date.
  • MERCHANT_REQUESTED -- the payee terminated the recurring billing arrangement. PSD2 Article 72 and contractual terms apply. Does NOT trigger consumer-revocation refund-window obligations on already-settled debits.
  • COMPLIANCE_TERMINATED -- the operator (gateway, facilitator, bank, regulator) forced termination from a post-mandate compliance trigger: sanctions hit on payer, KYC failure, AML alert, court order, regulator directive. Triggers POCA s.330 and AML 5+6 audit-chain linkage back to the originating compliance event.
  • EXPIRED -- the mandate reached its agreed end-date or maximum-execution count. No party-initiated decision; the mandate's own terms terminated it. Standard record-keeping only.

The four-element enumeration is closed. Implementations MUST reject any other value at validation time before canonicalisation. Free-form "reason" strings, dispute codes, or operator-internal classification labels are not acceptable substitutes for the categorical outcome.

The regulatory distinction is load-bearing. The four-value enumeration is one wider than the three-value enums in sibling formats because the regulatorily-load-bearing distinctions in mandate termination are genuinely four-state: payer vs payee vs operator vs time.

3.2. cancellation_provider_did

A string-valued DID URI identifying the entity issuing the cancellation receipt (gateway, facilitator, payer-bank, operator).

3.3. cancellation_timestamp_ms

An integer-valued field carrying the epoch-millisecond timestamp at which the cancellation event was observed and recorded by the issuing provider, in UTC.

This field MUST be an integer. RFC 3339 string forms (e.g. "2026-05-30T12:00:00Z") MUST be rejected at the validation layer before canonicalisation. This is Substrate Rule 2, normatively specified in draft-hopley-x402-canonicalisation-jcs Section 4.1.

3.4. effective_from_ms

An integer-valued field carrying the epoch-millisecond timestamp at which the cancellation takes legal effect, in UTC.

effective_from_ms MUST be greater than or equal to cancellation_timestamp_ms. Implementations MUST reject receipts where the effective time precedes the recording time, both at validation time and at verification time.

For most cancellations the two timestamps are equal. The independent encoding supports PSD2 Article 64(3)(a) direct-debit revocation timing, where the agreed effective time is typically the end of the working day before the next scheduled execution -- distinct from the moment the revocation was recorded.

For COMPLIANCE_TERMINATED outcomes the effective time MAY be immediate (equal to the recording time) or scheduled (regulator-directed future effective date).

Substrate Rule 2 applies: integer-only, RFC 3339 string forms rejected.

3.5. jurisdiction_flags

An ordered array of string-valued ISO-3166-1 alpha-2 country codes or alpha-3 region codes identifying the applicable regulatory frameworks for the cancellation event.

Authoring convention: primary jurisdiction first (where the operating entity is licensed), secondary jurisdictions in order of regulatory precedence.

Array element ORDER is SIGNIFICANT and load-bearing per draft-hopley-x402-canonicalisation-jcs Section 4.3.

3.6. mandate_ref

A string-valued field of the form sha256:<lowercase-hex-64>. The hex digest is SHA-256 of the JCS-canonical bytes of the mandate record being cancelled.

When the mandate was admitted under a compliance receipt (per draft-hopley-x402-compliance-receipt), the mandate_ref MAY equal the content_hash of that compliance receipt. This is the conventional choice and enables the audit-chain composition described in Section 5.

When the original mandate record is an operator-specific format (AP2 mandate object, MPP subscription record, custom recurring authorisation), the mandate_ref is the SHA-256 of that record's JCS-canonical bytes.

Implementations MUST NOT strip the sha256: prefix during canonicalisation or verification.

3.7. canon_version

A string-valued in-band canonicalisation rule pin. For this version of the receipt format the value MUST be jcs-rfc8785-v1.

4. Canonicalisation

The cancellation receipt MUST be canonicalised under the discipline pinned by draft-hopley-x402-canonicalisation-jcs and identified by the URN:

urn:x402:canonicalisation:jcs-rfc8785-v1

The full normative specification of the discipline (JCS RFC 8785 plus the schema-normalisation requirements including Substrate Rule 2) is in that document. This document does not redefine the discipline inline.

5. Audit Chain Composition

A cancellation receipt MAY participate in an audit chain alongside compliance receipts, settlement attestations, refund receipts, and other receipt classes that pin the same canonicalisation discipline.

5.1. Chain Row Shape

The audit chain row shape used by this document is identical to that specified in draft-hopley-x402-compliance-receipt Section 5.1 and reused by the settlement attestation (draft-hopley-x402-settlement-attestation) and refund receipt (draft-hopley-x402-refund-receipt) formats. The row shape is:

{
  "row_number": 1,
  "content_hash": "<hex64>",
  "prev_hash": "<hex64>",
  "row_content_hash": "<hex64>"
}

Row 1's prev_hash MUST be 64 zero hex characters. Row N's prev_hash MUST equal row N-1's row_content_hash.

5.2. Linkage Verification

Per draft-hopley-x402-compliance-receipt Section 5.2: a verifier reading a chain segment recomputes each row's row_content_hash from its first three fields and confirms forward linkage via prev_hash. Any mismatch indicates tampering or chain integrity loss.

5.3. Composition with Compliance Receipts

When a cancellation receipt references a compliance receipt via mandate_ref, the audit-chain composition is:

chain row N      chain row N+1
+------------+   +---------------+
| compliance |-->| cancellation  |
| receipt    |   | receipt       |
| (ALLOW)    |   | (USER_REQ)    |
+------------+   +---------------+

Row N anchors the compliance receipt admitting the mandate. Row N+1 anchors the cancellation receipt. The cancellation receipt's mandate_ref equals row N's content_hash. Chain linkage via prev_hash confirms ordering.

5.4. Composition with Settlement Attestations

For mandates with intervening recurring executions, settlement attestations occupy rows between the compliance receipt and the cancellation receipt:

chain row N      chain row N+1     chain row N+2    chain row N+3
+------------+   +-------------+   +-------------+  +---------------+
| compliance |-->| settlement  |-->| settlement  |->| cancellation  |
| receipt    |   | attestation |   | attestation |  | receipt       |
| (ALLOW)    |   | (SETTLED)   |   | (SETTLED)   |  | (USER_REQ)    |
+------------+   +-------------+   +-------------+  +---------------+
       row N           row N+1           row N+2          row N+3

A verifier walking the chain confirms the full mandate lifecycle under one canonicalisation pin.

5.5. Composition with Refund Receipts

When a USER_REQUESTED cancellation triggers a refund obligation under PSD2 Article 64 (refund of a recently-settled debit that predated the cancellation but post-dated the effective revocation window), a refund receipt MAY follow:

chain row N+3        chain row N+4
+---------------+    +------------+
| cancellation  |--->| refund     |
| receipt       |    | receipt    |
| (USER_REQ)    |    | (FULL)     |
+---------------+    +------------+

The refund receipt's original_payment_ref references the settlement attestation being refunded (not the cancellation receipt). The cancellation receipt is the chain-evidence anchor that establishes why the refund is owed.

6. Year-N Auditability Properties

The same six properties pinned by draft-hopley-x402-canonicalisation-jcs Section 5 apply to the cancellation receipt:

  1. Self-describing canonicalisation pin via canon_version.
  2. No external rule registry required.
  3. Cross-implementation verifiability (8-implementation matrix per the discipline I-D).
  4. Tamper detection via per-row content_hash and chain prev_hash linkage.
  5. Regulatory distinction preserved via closed enumeration.

Plus one cancellation-specific property:

  1. Mandate-cancellation evidence chain. A verifier reading a retained cancellation receipt years after emission can determine (a) which mandate was cancelled (via mandate_ref), (b) who cancelled it (via the combination of cancellation_reason and cancellation_provider_did), (c) when the cancellation was recorded (cancellation_timestamp_ms), and (d) when it became effective (effective_from_ms), without dependence on the issuing operator's continued operation.

7. Composition with Other x402 Substrate

7.1. Compliance Receipt Linkage

See Section 5.3. The conventional mandate_ref target for a mandate admitted under a compliance receipt is the content_hash of that compliance receipt.

See Section 5.4. Settlement attestations recording recurring executions occupy chain rows between the admission and the cancellation. The cancellation receipt does not reference individual settlement attestations directly; chain linkage via prev_hash establishes ordering.

7.3. Refund Receipt Linkage

See Section 5.5. A USER_REQUESTED cancellation MAY be followed in the chain by a refund receipt if PSD2 Article 64 refund obligations attach to a recently-settled debit.

7.4. Non-Goals

This document does not encode:

  • The mandate's terms (frequency, cap, expiry condition). Those belong in the mandate record itself.
  • The refund obligation determination. PSD2 Article 64 refund-window applicability is verifier-side judgement against retained settlement attestations.
  • The compliance event driving a COMPLIANCE_TERMINATED outcome. That belongs in a separate compliance receipt linked via the audit chain.

8. IANA Considerations

8.1. URN Namespace Registration

This document references the URN urn:x402:canonicalisation:jcs-rfc8785-v1 registered by draft-hopley-x402-canonicalisation-jcs Section 10.1. No additional URN namespace registration is required by this document.

8.2. Receipt Format Identifier

This document defines the receipt format identifier:

urn:x402:receipt:cancellation-receipt-v1

This identifier MAY be used by composite-trust-query implementations to refer to cancellation receipts as a class. Registration with IANA is requested under the x402 URN namespace.

9. Security Considerations

9.1. Receipt Tampering

A cancellation receipt's content_hash is the SHA-256 of its JCS-canonical bytes. Tampering with any field produces a different hash; the tampered receipt fails verification against any audit-chain row referencing the original content_hash.

9.2. Backdated Cancellation

The two-timestamp design (cancellation_timestamp_ms recording event time, effective_from_ms recording legal effective time) admits a class of attack where a malicious operator emits a receipt at time T with effective_from_ms set to a past timestamp T' < T, to retroactively void a debit that has already settled.

Mitigation is verifier-side: a verifier MUST cross-check the cancellation_timestamp_ms against operator-emission-time evidence (TLS log, audit-chain prev_hash of the row recording this receipt, external timestamping service) before accepting a claimed effective time in the past.

The effective_from_ms >= cancellation_timestamp_ms invariant required by Section 3.4 prevents the simpler attack of stamping the recording time in the past, but does not by itself prevent all backdating attacks.

9.3. Reason Spoofing

A malicious operator could emit a MERCHANT_REQUESTED receipt for what was actually a USER_REQUESTED cancellation, to avoid the PSD2 Article 64 refund-window obligation. Detection requires out-of-band evidence (payer complaint, payer-side log, regulator inspection). The cancellation_provider_did identifies the attesting party, supporting accountability.

9.4. Compliance-Terminated Receipt Disclosure

A COMPLIANCE_TERMINATED receipt records that a compliance trigger fired against the payer. Such a receipt MAY contain indirectly-disclosing information: the existence of the cancellation under that reason, combined with public sanctions listing dates, MAY reveal that the payer was placed on a sanctions list.

Implementations SHOULD restrict access to COMPLIANCE_TERMINATED receipts to parties with a legitimate audit interest (regulator, auditor, court order). Public disclosure of such receipts is NOT in scope of this document.

9.5. Operator Continuity Loss

If the original attesting operator becomes unavailable, the audit chain and its cancellation receipts MUST remain independently verifiable from retained bytes plus the reference implementations cited in draft-hopley-x402-canonicalisation-jcs Section 7.

Appendix A. References

A.1. Normative References

  • [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
  • [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
  • [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017.
  • [RFC8785] Rundgren, A., Jordan, B., and S. Erdtman, "JSON Canonicalization Scheme (JCS)", RFC 8785, DOI 10.17487/RFC8785, June 2020.
  • draft-hopley-x402-canonicalisation-jcs Hopley, C., "JCS Canonicalisation Discipline for Agentic-Payment Receipts", draft-hopley-x402-canonicalisation-jcs-v1, May 2026.

A.2. Informative References

  • draft-hopley-x402-compliance-receipt Hopley, C., "Categorical Compliance Screening Receipt Format for Agentic-Payment Flows", draft-hopley-x402-compliance-receipt-00, May 2026.
  • draft-hopley-x402-settlement-attestation Hopley, C., "Categorical Settlement Attestation Format for Agentic-Payment Flows", draft-hopley-x402-settlement-attestation-00, May 2026.
  • draft-hopley-x402-refund-receipt Hopley, C., "Categorical Refund Receipt Format for Agentic-Payment Flows", draft-hopley-x402-refund-receipt-00, May 2026.
  • [AlgoVoi-Substrate-Authorship] AlgoVoi, "Substrate Authorship and Provenance", target="https://docs.algovoi.co.uk/substrate-authorship-provenance"
  • EU Payment Services Directive 2 (PSD2, Directive 2015/2366), Articles 64, 72, 89.
  • EU Markets in Crypto-Assets Regulation (MiCA, Regulation (EU) 2023/1114), Article 80.
  • EU Anti-Money Laundering Regulation (AMLR, Regulation (EU) 2024/1624), Article 56.
  • EU Anti-Money Laundering Directive 5 (Directive (EU) 2018/843).
  • EU Anti-Money Laundering Directive 6 (Directive (EU) 2018/1673).
  • UK Proceeds of Crime Act 2002, section 330.
  • UK Consumer Rights Act 2015.

Appendix B. Appendix A. Examples (Informative)

B.1. A.1. USER_REQUESTED revocation under PSD2 Article 64 

{
  "canon_version": "jcs-rfc8785-v1",
  "cancellation_provider_did": "did:web:api.algovoi.co.uk",
  "cancellation_reason": "USER_REQUESTED",
  "cancellation_timestamp_ms": 1716494400000,
  "effective_from_ms": 1716537600000,
  "jurisdiction_flags": ["UK", "EU"],
  "mandate_ref": "sha256:0dd5d0b76c9b9281fdeb2509ad38ab132b16a17385ca01d976ff9e6e12563a0f"
}

Records a payer-initiated revocation under PSD2 Article 64 with effective time set to end-of-business-day prior to the next scheduled execution per Article 64(3)(a). If a debit already settled within the recoverable window prior to the effective date, a refund receipt MAY follow.

B.2. A.2. MERCHANT_REQUESTED termination under PSD2 Article 72 

{
  "canon_version": "jcs-rfc8785-v1",
  "cancellation_provider_did": "did:web:api.algovoi.co.uk",
  "cancellation_reason": "MERCHANT_REQUESTED",
  "cancellation_timestamp_ms": 1716494400000,
  "effective_from_ms": 1716537600000,
  "jurisdiction_flags": ["UK", "EU"],
  "mandate_ref": "sha256:0dd5d0b76c9b9281fdeb2509ad38ab132b16a17385ca01d976ff9e6e12563a0f"
}

Records payee-initiated termination of the recurring billing arrangement. Does not trigger the Article 64 refund-window obligation on already-settled debits.

B.3. A.3. COMPLIANCE_TERMINATED under sanctions hit 

{
  "canon_version": "jcs-rfc8785-v1",
  "cancellation_provider_did": "did:web:api.algovoi.co.uk",
  "cancellation_reason": "COMPLIANCE_TERMINATED",
  "cancellation_timestamp_ms": 1716494400000,
  "effective_from_ms": 1716494400000,
  "jurisdiction_flags": ["UK", "EU"],
  "mandate_ref": "sha256:0dd5d0b76c9b9281fdeb2509ad38ab132b16a17385ca01d976ff9e6e12563a0f"
}

Records immediate operator-forced termination. Effective time equals recording time. Anchors POCA s.330 and AML 5+6 audit-chain linkage back to the originating compliance receipt (a separate record).

B.4. A.4. EXPIRED at agreed mandate end-date 

{
  "canon_version": "jcs-rfc8785-v1",
  "cancellation_provider_did": "did:web:api.algovoi.co.uk",
  "cancellation_reason": "EXPIRED",
  "cancellation_timestamp_ms": 1716494400000,
  "effective_from_ms": 1716494400000,
  "jurisdiction_flags": ["UK", "EU"],
  "mandate_ref": "sha256:0dd5d0b76c9b9281fdeb2509ad38ab132b16a17385ca01d976ff9e6e12563a0f"
}

Records time-based expiry of the mandate. Standard record-keeping only; no further regulatory action attaches.

Appendix C. Appendix B. Reference Implementations (Informative)

The following open-source implementations conform to this format:

Conformance vectors:

https://github.com/chopmob-cloud/algovoi-jcs-conformance-vectors/tree/main/vectors/cancellation_receipt_v1

8 byte-level reference vectors + 7 pair invariants + 3 chain invariants pinning the closed four-element enumeration, jurisdiction-array-order, canon_version pin, effective-time-greater-equal-recording-time invariant, and audit-chain linkage properties.

Appendix D. Known Adopters (Informative)

The following downstream parties have published artefacts that anchor to the cancellation receipt format specified by this document, or to the canonicalisation discipline shared with this format. Inclusion in this list is informational and reflects public adoption only; it does not imply endorsement or normative authority from the listed party.

Table 1
Adopter Surface Anchor
AlgoVoi (api.algovoi.co.uk) Production mandate-lifecycle issuer All AlgoVoi-emitted cancellation receipts under canon_version: jcs-rfc8785-v1

Adopters publishing vector sets or receipt-format extensions that anchor to this format are encouraged to publish them in adopter-controlled repositories with canon_version recorded in-band, so each adopter's authorship is unambiguous and their artefact is independently citable.

This appendix is maintained as a record of observed adoption at the time of revision; absence from this list is not normative.

Appendix E. Acknowledgments

This document, the receipt format it specifies, and the conformance vectors derived from it are AlgoVoi work under AlgoVoi authorship. Substrate authorship history is catalogued at target="https://docs.algovoi.co.uk/substrate-authorship-provenance".

The canonicalisation discipline pinned by Section 4 is normatively specified in draft-hopley-x402-canonicalisation-jcs under the same authorship.

This document closes the lifecycle gap between the admission-time compliance receipt (draft-hopley-x402-compliance-receipt), per-execution settlement attestation (draft-hopley-x402-settlement-attestation), and post-cancellation refund receipt (draft-hopley-x402-refund-receipt) formats. The four formats share the same canonicalisation pin, audit-chain row shape, and integer-millisecond timestamp encoding, so that a verifier walking the full mandate lifecycle requires only one implementation of the canonicalisation discipline.

The author acknowledges Anders Rundgren as the editor of RFC 8785, the JSON Canonicalization Scheme on which the discipline builds.

Author's Address

Christopher Hopley
AlgoVoi