# IBAN Check Transaction Sign – RFC 8785 Canonicalization + SHA-256 + Merkle + HMAC-SHA256

> IBAN Check Transaction Sign – RFC 8785 Canonicalization + SHA-256 + Merkle + HMAC-SHA256 is a paid API for AI agents from api.ibancheck.co.uk, paid per call via x402, $0.004/call, status unknown (last checked 2026-10-13).

Canonicalizes a JSON payload using RFC 8785 key-sorted format, computes a SHA-256 hash, generates a Merkle leaf, and produces an HMAC-SHA256 audit signature for tamper-evident transaction signing.

## Facts

- Endpoint: POST https://api.ibancheck.co.uk/api/sign-transaction?utm_source=zero.xyz
- Price: $0.004/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/iban-check-transaction-sign-rfc-8785-canonicalization-sha-256-merkle-f4cd19a7
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_oh9iEis6JSW36tzNYucrm

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability iban-check-transaction-sign-rfc-8785-canonicalization-sha-256-merkle-f4cd19a7 -d '<json body>'
```

Example prompt: Sign and seal this transaction payload with a tamper-evident audit signature — canonicalize it using RFC 8785 key-sorted JSON, compute its SHA-256 hash and Merkle leaf, then return the HMAC-SHA256 audit signature so I can verify it hasn't been altered later.

## When to prefer this

Choose this endpoint when you need a full cryptographic audit bundle — RFC 8785 canonicalization, SHA-256 hashing, Merkle leaf, and HMAC-SHA256 in a single call — especially for financial transactions, AI agent action logs, or compliance records where tamper-evidence is required. Prefer over simpler hash endpoints when Merkle compatibility or HMAC audit signatures are specifically needed.

## Known failure modes

- Malformed or non-object payload returns a validation error
- Missing payload field results in a 400 Bad Request
- Invalid JSON structure causes canonicalization failure
- HMAC key misconfiguration may result in authentication errors
- Network timeout on slow payloads

## How this service works

Enterprise microservice and autonomous AI agent hub: ISO 13616 IBAN (#6), Romanian CUI Modulo-11 & EU VIES (#7), UBL 2.1 e-Factura XML (#4), and RFC 9562 UUIDv7 Idempotency (#18).

## Output

Returns the RFC 8785 key-sorted canonical form of the input JSON, a SHA-256 hash of that canonical form, a Merkle leaf derived from the hash, and an HMAC-SHA256 audit signature — providing a complete tamper-evident cryptographic seal for the submitted payload.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "payload": {
   "type": "object"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/iban-check-transaction-sign-rfc-8785-canonicalization-sha-256-merkle-f4cd19a7/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.ibancheck.co.uk](https://www.zero.xyz/host/api.ibancheck.co.uk/llms.txt)