# Proofwork Base USDC Receipt Verifier

> Proofwork Base USDC Receipt Verifier is a paid API for AI agents from proofwork-the402-webhook.phase-voice.workers.dev, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-15).

Verifies a specific Circle USDC payment on Base mainnet by checking a transaction hash against an expected recipient and amount, returning finalized chain evidence.

## Facts

- Endpoint: GET https://proofwork-the402-webhook.phase-voice.workers.dev/v1/base-usdc-receipt
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/proofwork-base-usdc-receipt-verifier-2651293a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_1C8wfWVoXIFKQHb78C6ry

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 proofwork-base-usdc-receipt-verifier-2651293a
```

Example prompt: Can you verify that transaction 0x4a3b...f9e2 on Base mainnet actually sent 12.50 USDC to wallet 0xAbCd...1234 and confirm it's finalized?

## When to prefer this

Use this endpoint when you need cryptographic, on-chain proof that a specific USDC payment occurred on Base mainnet with exact recipient and amount matching. Prefer it over general blockchain explorers when you need a structured, machine-readable verdict with finality confirmation — ideal for automated payment gating, invoice reconciliation, or dispute resolution in agent workflows where trust in payment receipt must be verifiable without a centralized payment processor.

## Known failure modes

- Transaction hash not found on Base mainnet — returns unconfirmed or error verdict
- Expected amount or recipient does not match on-chain data — returns verdict indicating mismatch
- Transaction exists but is not yet finalized — returns pending finality status
- Malformed transaction hash (not 0x + 64 hex chars) — schema validation error
- Invalid recipient address format — schema validation error
- Amount format exceeds allowed precision or length — validation rejection

## How this service works

Small non-cyber evidence and data APIs payable per request with x402 on Base.

## Output

Returns a JSON object with a 'verdict' field (e.g. 'confirmed'), a 'confirmed' boolean, a 'finality' field indicating chain finality status (e.g. 'finalized'), an 'evidence' array of supporting on-chain data, and an 'observed' object with raw transaction details. Agents can use 'confirmed: true' and 'finality: finalized' together to conclusively prove payment occurred.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "queryParams"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "transaction_hash"
     ],
     "properties": {
      "transaction_hash": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]{64}$"
      },
      "expected_recipient": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]{40}$"
      },
      "expected_amount_usdc": {
       "type": "string",
       "pattern": "^(?:0|[1-9][0-9]{0,11})(?:\\.[0-9]{1,6})?$"
      }
     },
     "additionalProperties": false
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "mode": "inspect",
  "verdict": "observed",
  "evidence": [],
  "finality": "finalized",
  "observed": {},
  "confirmed": true,
  "transaction": {}
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/proofwork-base-usdc-receipt-verifier-2651293a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from proofwork-the402-webhook.phase-voice.workers.dev](https://www.zero.xyz/host/proofwork-the402-webhook.phase-voice.workers.dev/llms.txt)