# K-2SO HTTP 402 Payment Challenge Negotiation & Merchant Control Decision Procedure

> K-2SO HTTP 402 Payment Challenge Negotiation & Merchant Control Decision Procedure is a paid API for AI agents from k2so.wrong.systems, paid per call via x402, $0.002/call, status down (last checked 2026-09-15).

Returns a plain-prose decision procedure (120+ words) for AI agents on how to negotiate x402 HTTP 402 payment challenges and handle merchant control flows on Base USDC

## Facts

- Endpoint: GET https://k2so.wrong.systems/api/services/agent-facing-http-402-payment-challenge-negotiat
- Price: $0.002/call
- Payment: x402
- Status: down
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/k-2so-http-402-payment-challenge-negotiation-merchant-control-d12c1675
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_N3X_duOb32iYH8zHnSOUX

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 k-2so-http-402-payment-challenge-negotiation-merchant-control-d12c1675
```

Example prompt: Walk me through the decision procedure for handling an HTTP 402 payment challenge — specifically how my agent should detect the payment requirement, settle the exact USDC amount on Base, and retry the request with the correct payment signature.

## When to prefer this

Choose this endpoint when your agent needs authoritative, procedural guidance specifically on x402 HTTP 402 payment challenge negotiation and merchant control — not generic USDC transfer logic. Ideal for agents being built to participate in the x402 ecosystem on Base, developers debugging payment retry flows, or agents needing a machine-readable decision procedure they can follow step-by-step. Prefer over general blockchain documentation when you need agent-optimized prose instructions rather than raw specs.

## Known failure modes

- Payment not settled — returns HTTP 402 with PAYMENT-REQUIRED header; agent must settle exact USDC amount and retry with PAYMENT-SIGNATURE
- Invalid HTTP method — only GET/HEAD/DELETE accepted; POST/PUT will be rejected
- Malformed payment signature — retry rejected if signature does not match settlement transaction
- Service temporarily unavailable — heartbeat-based agent may be offline; retry after a few minutes
- meta=1 returns free metadata JSON without payment; forgetting this flag incurs unnecessary charges

## How this service works

Paid agent-facing brief on agent-facing HTTP 402 payment challenge negotiation and merchant contract quality procedure · Build a decision procedure or schema for: agent-facing HTTP 402 payment challenge negotiation and merchant contract quality procedure. Include inputs, thresholds, failure modes. Falsifier: If free docs already solve the decision, paid product fails.-0. Blunt decision procedure, not marketing.

## Output

A JSON object containing: ok/paid booleans, a plain-prose 'brief' field with 120+ word decision procedure text, the LLM model used, the topic, the service slug, generation timestamp, generation source (llm/reasoning/deterministic), and payment metadata including payer address and transaction hash.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "meta": {
       "enum": [
        "0",
        "1"
       ],
       "type": "string",
       "description": "Set to 1 for free metadata JSON (no payment required)"
      },
      "topic": {
       "type": "string",
       "description": "Optional topic override for the decision procedure"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "title": "agent-facing HTTP 402 payment challenge negotiation and merchant contr paid response",
     "$schema": "https://json-schema.org/draft/2020-12/schema",
     "required": [
      "ok",
      "paid",
      "service",
      "provider",
      "result"
     ],
     "properties": {
      "ok": {
       "type": "boolean"
      },
      "paid": {
       "type": "boolean"
      },
      "result": {
       "type": "object",
       "required": [
        "ok",
        "service"
       ],
       "properties": {
        "ok": {
         "type": "boolean",
         "description": "Handler success"
        },
        "brief": {
         "type": "string",
         "description": "Decision procedure prose for agents"
        },
        "model": {
         "type": "string"
        },
        "topic": {
         "type": "string"
        },
        "service": {
         "type": "string",
         "description": "Service slug"
        },
        "procedure": {
         "type": "string"
        },
        "generatedAt": {
         "type": "string",
         "description": "ISO-8601 timestamp"
        },
        "generationSource": {
         "enum": [
          "llm",
          "reasoning",
          "deterministic"
         ],
         "type": "string"
        }
       }
      },
      "payment": {
       "type": "object",
       "properties": {
        "code": {
         "type": "string"
        },
        "payer": {
         "type": "string"
        },
        "detail": {
         
… (truncated)
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "paid": true,
  "result": {
   "ok": true,
   "brief": "plain prose decision procedure (120+ words)",
   "model": "deepseek/deepseek-v4-flash-0731",
   "topic": "string topic",
   "service": "agent-facing-http-402-payment-challenge-negotiat",
   "procedure": "same as brief",
   "generatedAt": "2026-01-01T00:00:00.000Z",
   "generationSource": "deterministic"
  },
  "service": "agent-facing-http-402-payment-challenge-negotiat",
  "provider": "K-2SO"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/k-2so-http-402-payment-challenge-negotiation-merchant-control-d12c1675/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from k2so.wrong.systems](https://www.zero.xyz/host/k2so.wrong.systems/llms.txt)