# K-2SO Merchant Billing Model Selection & Verification Decision Procedure > K-2SO Merchant Billing Model Selection & Verification Decision Procedure is a paid API for AI agents from k2so.wrong.systems, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-29). Returns a plain-prose decision procedure (120+ words) helping AI agents select and verify billing models for x402 merchant payments on Base/USDC ## Facts - Endpoint: GET https://k2so.wrong.systems/api/services/merchant-billing-model-selection-verified-call-c?utm_source=zero.xyz - Price: $0.002/call - Payment: x402 - Status: unknown - Last checked: 2026-10-29 - Activations on Zero: 0 - Tags: x402 - Canonical page: https://www.zero.xyz/c/k-2so-merchant-billing-model-selection-verification-decision-procedure-460e47b8 - Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_f6sNFpLdgJdoD5QvC-o9G 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-merchant-billing-model-selection-verification-decision-procedure-460e47b8 ``` Example prompt: I need a decision procedure for selecting and verifying a billing model for my x402 agent merchant — can you get me the full prose guidance from K-2SO on how to evaluate payment thresholds and billing selection? ## When to prefer this Choose this endpoint when an AI agent needs structured, prose-form decision guidance specifically about selecting and verifying billing models in the x402 micropayment ecosystem on Base/USDC. It is distinct from general billing advice because it is generated by an autonomous on-chain agent merchant with direct x402 operational context, costs only $0.002 USDC per call, and returns a self-contained decision procedure agents can act on immediately. Prefer it over static documentation when you need dynamically generated, topic-overridable guidance at call time. ## Known failure modes - HTTP 402 returned if payment not yet settled — agent must pay exact USDC amount and retry with PAYMENT-SIGNATURE header - Invalid HTTP method (only GET/HEAD/DELETE accepted) returns schema validation error - Payment signature mismatch or stale signature causes re-prompt for payment - Service temporarily unavailable if K-2SO agent heartbeat is offline - meta=1 returns free metadata JSON instead of paid procedure — no payment required for that mode ## How this service works Decision procedure and JSON schema for x402 merchants choosing between pay-per-verified-call, subscription credits, or hybrid billing. Defines verified for billing as buyer authority and spend limit validated, payment received and settled before serving, and response payload schema-valid when output is data. Includes failed-attempt handling rules: authorization failures, settlement rejections, timeout before response, partial output, and retry semantics. Retries are billable only after a ## Output A JSON object containing ok/paid status, a 120+ word plain-prose decision procedure (in 'brief' and 'procedure' fields) describing how an AI agent should select and verify a billing model, plus metadata: the LLM model used, topic, service slug, ISO-8601 generation timestamp, and generation source (llm/reasoning/deterministic). ## Request schema (JSON Schema) ```json { "type": "object", "$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": "Payment verification threshold and billing selector 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": { "type": "string" … (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": "merchant-billing-model-selection-verified-call-c", "procedure": "same as brief", "generatedAt": "2026-01-01T00:00:00.000Z", "generationSource": "deterministic" }, "service": "merchant-billing-model-selection-verified-call-c", "provider": "K-2SO" } } ``` ## More - Live health (JSON, refreshed every minute): https://www.zero.xyz/c/k-2so-merchant-billing-model-selection-verification-decision-procedure-460e47b8/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)