# Agent Vending Machine - Hash Attestation

> Agent Vending Machine - Hash Attestation is a paid API for AI agents from agent-vending-machine.avm-7301.workers.dev, paid per call via x402, $0.05/call, status unknown (last checked 2026-09-15).

Submits a SHA-256 hash or raw payload and receives a signed Ed25519 receipt binding the hash to a timestamp, providing third-party existence attestation.

## Facts

- Endpoint: POST https://agent-vending-machine.avm-7301.workers.dev/attest
- Price: $0.05/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agent-vending-machine-hash-attestation-67773bc6
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Pssnu0XMSQUeSqFJBCrJk

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 agent-vending-machine-hash-attestation-67773bc6 -d '<json body>'
```

Example prompt: I need a signed existence proof for this document — please attest the SHA-256 hash a3f1c2d4e5b67890abcdef1234567890abcdef1234567890abcdef1234567890ab and give me a timestamped Ed25519-signed receipt I can use as third-party proof it existed right now.

## When to prefer this

Use this endpoint when you need a cryptographically signed, third-party-attested timestamp receipt for a hash or payload — especially for legal, audit, or compliance purposes where you need an independent party's Ed25519 signature binding content to a moment in time. Prefer this over self-signed or chain-based solutions when you want a lightweight, verifiable receipt without blockchain overhead.

## Known failure modes

- Invalid sha256 format (not 64 lowercase hex chars) — returns 400 error
- Neither sha256 nor payload provided — returns 400 missing parameter error
- Both sha256 and payload provided simultaneously — may return 400 ambiguous input error
- Payment not included or insufficient USDC — returns 402 Payment Required
- Service temporarily unavailable — returns 503

## How this service works

Third-party existence attestation: submit a sha256 hash (or a payload to hash) and receive an Ed25519-signed receipt binding the hash to an issuance timestamp. Verify any receipt for free at /verify; signing public key published at /.

## Output

An Ed25519-signed receipt object binding the submitted hash (or the server-side hash of the provided payload) to an issuance timestamp, serving as cryptographic third-party proof of existence at that moment. The receipt can be independently verified for free at the /verify endpoint.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "sha256": {
   "type": "string",
   "description": "Lowercase hex sha256 digest to attest (64 chars). Provide this or `payload`."
  },
  "payload": {
   "type": "string",
   "description": "Raw UTF-8 payload; the service hashes it server-side. Provide this or `sha256`."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agent-vending-machine-hash-attestation-67773bc6/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agent-vending-machine.avm-7301.workers.dev](https://www.zero.xyz/host/agent-vending-machine.avm-7301.workers.dev/llms.txt)