# SignGate Agent Buyer Identity Preflight | x402 Purchase Governance

> SignGate Agent Buyer Identity Preflight | x402 Purchase Governance is a paid API for AI agents from base-agent-preflight.bytoken2023.workers.dev, paid per call via x402, $0.15/call, status unknown (last checked 2026-09-14).

Performs a pre-payment risk assessment for AI agents about to make an x402 USDC payment, checking buyer identity, amount limits, recipient allowlists/blocklists, and approval policies before authorizing the transaction.

## Facts

- Endpoint: GET https://base-agent-preflight.bytoken2023.workers.dev/v1/x402/agent/payment-risk-gateway
- Price: $0.15/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/signgate-agent-buyer-identity-preflight-x402-purchase-governance-b9821757
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_dDcyZ37v7vmnPiqhcgj04

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 signgate-agent-buyer-identity-preflight-x402-purchase-governance-b9821757
```

Example prompt: Before my agent pays 25 USDC to wallet 0xAb3f9c2d1e4B7a6F0C8d2E5f1A3b4C7d9E0f1A2b for accessing a dataset (request ID req-agent-42x, nonce abc123def456, purpose 'dataset-access-audit'), run a SignGate preflight risk check to make sure this payment is safe and within policy.

## When to prefer this

Use this endpoint when an AI agent is about to autonomously execute an x402 USDC payment and you need a policy-aware pre-authorization check before funds move. It is specifically designed for the x402 payment protocol on Base (EVM), supporting recipient allowlists/blocklists, per-transaction amount caps, human escalation thresholds, and audit trails via invoice binding. Prefer this over generic compliance APIs when your agent operates in an x402-native environment and you need lightweight, per-call governance at $0.15 USDC without heavy KYC infrastructure.

## Known failure modes

- Missing required query parameters (request_id, agent_id, purpose, pay_to, amount_usdc, nonce) returns a validation error
- Invalid Ethereum address format for pay_to returns a pattern mismatch error
- Malformed nonce or request_id not matching pattern returns schema validation failure
- Risk score returned as 'high' may block the payment intent without explicit error
- Service unavailable on Cloudflare Workers edge may return 5xx timeout
- Recipient on block_pay_to list results in flagged or rejected assessment

## How this service works

Machine-payable service intelligence for discovering, verifying, and monitoring identity, risk, authorization, execution-preflight, and evidence APIs before autonomous agents spend.

## Output

Returns a JSON object containing a risk assessment with a risk_level (e.g. 'low', 'medium', 'high'), a numeric risk_score, an array of flags indicating any triggered policy rules, the network identifier (e.g. 'eip155:8453' for Base), and the product name. This tells the agent whether to proceed with payment, block it, or escalate for human review.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "request_id",
      "agent_id",
      "purpose",
      "pay_to",
      "amount_usdc",
      "nonce"
     ],
     "properties": {
      "nonce": {
       "type": "string",
       "pattern": "^[A-Za-z0-9._:-]{8,128}$",
       "description": "Replay-prevention nonce."
      },
      "pay_to": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]{40}$",
       "description": "Recipient address."
      },
      "purpose": {
       "type": "string",
       "maxLength": 80,
       "description": "Short audit purpose for the payment."
      },
      "agent_id": {
       "type": "string",
       "pattern": "^[A-Za-z0-9._:-]{1,96}$",
       "description": "AI agent or runtime requesting payment authorization."
      },
      "invoice_id": {
       "type": "string",
       "maxLength": 160,
       "description": "Commercial context binding the payment to an invoice or order."
      },
      "request_id": {
       "type": "string",
       "pattern": "^[A-Za-z0-9._:-]{1,128}$",
       "description": "Caller-defined idempotency key for the intent."
      },
      "risk_score": {
       "type": "string",
       "pattern": "^[0-9]{1,3}$",
       "description": "Caller-supplied recipient risk score from 0 to 100."
      },
      "amount_usdc": {
       "type": "string",
       "pattern": "^[0-9]+(?:\\.[0-9]{1,6})?$",
       "description": "Stablecoin amount in USDC."
      },
      "risk_labels": {
       "type": "string",
       "maxLength": 512,
       "description": "Optional comma-separated risk labels."
      },
      "allow_pay_to": {
       "type": "string",
       "maxLength": 2048,
       "description": "Optional comma-separated recipient allowlist."
      },
      "block_pay_to": {
       "type": "string",
       "maxLength": 2048,
       "description": "Optional comma-separated recipient blocklist."
      },
      "invoice_hash": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]{64}$",
       "description": "Optional invoice or order hash."
      },
      "max_single_usdc": {
       "type": "string",
       "pa
… (truncated)
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "network": "eip155:8453",
  "product": "agent-payment-risk-gateway",
  "assessment": {
   "flags": [],
   "risk_level": "low",
   "risk_score": 0
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/signgate-agent-buyer-identity-preflight-x402-purchase-governance-b9821757/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from base-agent-preflight.bytoken2023.workers.dev](https://www.zero.xyz/host/base-agent-preflight.bytoken2023.workers.dev/llms.txt)