# Wintergreen x402 Endpoint Migration Guide (API Key to x402)

> Wintergreen x402 Endpoint Migration Guide (API Key to x402) is a paid API for AI agents from x402.wintergreen.uk, paid per call via x402, $0.01/call, status down (last checked 2026-09-15).

Returns a payment-gated knowledge article explaining how to migrate from API-key authentication to the x402 micropayment protocol for AI agents.

## Facts

- Endpoint: GET https://x402.wintergreen.uk/api/v1/knowledge/endpoint-migration-apikey-to-x402
- Price: $0.01/call
- Payment: x402
- Status: down
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/wintergreen-x402-endpoint-migration-guide-api-key-to-x402-62abd5ae
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_tGJTQ26TiX-E781r1x_dz

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 wintergreen-x402-endpoint-migration-guide-api-key-to-x402-62abd5ae
```

Example prompt: Can you pull up the Wintergreen guide on migrating from API key authentication to x402 micropayments — I want to understand the step-by-step process for switching my API over to the EIP-712 payment flow?

## When to prefer this

Choose this endpoint when an AI agent or developer needs authoritative guidance on transitioning from API-key-based authentication to the x402 micropayment standard. It is specifically useful when building agent-native APIs that monetize via per-call crypto micropayments rather than subscription keys, and when the developer wants protocol-level detail on EIP-712 signing and x402 header conventions.

## Known failure modes

- HTTP 402 returned if payment header is missing or invalid — agent must sign EIP-712 and retry with X-PAYMENT header
- Invalid file or route slug returns empty or error response due to unspecified response schema
- Payment rejected if USDC balance insufficient on Base chain
- Network or RPC errors on Base chain causing payment verification failure
- Content unavailable if slug parameters do not match a known knowledge article

## How this service works

Payment-gated crypto trading intelligence for AI agents.
    
## Categories
- **Hyperliquid Signals**: Real-time funding divergence, lead-lag correlation, liquidation clusters, session volume area levels
- **Quant Methodology**: Backtesting walk-forward validation, strategy generation with kill battery (19 rules), risk management with Kelly sizing, regime detection, execution frameworks, agent orchestration
- **Market Insights**: 22 crypto microstructure observations — funding, liquidation, orderbook, regime, flow, anomaly
- **Power Markets**: ERCOT field guide, merit-order model, duck curve analysis
- **Career Guides**: Firefighter oral board prep, medical coding, ATSA, contractor estimating
- **Trust Scoring**: x402 endpoint verification, P2D badges

## Payment
All paid endpoints return HTTP 402 with USDC on Base (eip155:8453). 
Sign EIP-712 TransferWithAuthorization and retry with X-PAYMENT header.
PayTo: 0xAe9834d71F1Bd989A0dc17593451af823E31CeeD

## Output

A knowledge article (text/markdown or structured content) detailing the process of migrating an API from traditional API-key authentication to the x402 micropayment protocol, including EIP-712 TransferWithAuthorization signing, header conventions, and agent integration patterns. Returned after successful USDC payment of $1.50 on Base (eip155:8453).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "_file_slug": {
   "type": "string"
  },
  "_route_slug": {
   "type": "string"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/wintergreen-x402-endpoint-migration-guide-api-key-to-x402-62abd5ae/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402.wintergreen.uk](https://www.zero.xyz/host/x402.wintergreen.uk/llms.txt)