# Chit402 A2A Message — Paid LLM Inference with USDC Receipts

> Chit402 A2A Message — Paid LLM Inference with USDC Receipts is a paid API for AI agents from api.chit402.com, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-14).

Sends a chat completion request to a paid LLM endpoint over x402, deducting USDC per call and returning an OpenAI-compatible response with a verifiable receipt URL.

## Facts

- Endpoint: POST https://api.chit402.com/a2a-message
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/chit402-a2a-message-paid-llm-inference-with-usdc-receipts-871ac5ed
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_jXfxRXGBngg6vEPvPRxIX

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 chit402-a2a-message-paid-llm-inference-with-usdc-receipts-871ac5ed -d '<json body>'
```

Example prompt: Send a chat message to Chit402 using the xfuel/auto model — the message is 'Summarize the concept of zero-knowledge proofs in two sentences', cap it at 200 tokens, and give me back the response along with the receipt URL so I can verify the payment.

## When to prefer this

Choose this endpoint when your agent needs verifiable, auditable records of every LLM call with a linked payment receipt — ideal for multi-agent systems where spend accountability, policy compliance, or cost-plus billing evidence is required. Prefer it over generic LLM APIs when you need USDC micropayment settlement on Base or Solana, OpenAI-compatible message format, and a per-call receipt URL for treasury or audit purposes.

## Known failure modes

- Insufficient USDC balance — x402 payment fails before inference begins
- Invalid model ID — returns error if model string not found in /v1/models
- Malformed messages array — missing required `role` or `content` fields causes validation error
- Token budget exceeded — response truncated if max_tokens is too low
- Temperature out of range — values outside 0–2 rejected
- Network or payment gateway timeout — call fails with no receipt generated

## How this service works

Who paid which call — export, policy, evidence. Possession book for agent spend.

## Output

Returns an OpenAI-compatible chat completion JSON object containing the assistant's reply in `choices[0].message.content`, token usage breakdown (`prompt_tokens`, `completion_tokens`, `total_tokens`), the model used, a unique completion ID, and an `xfuel.verify_url` field linking to a verifiable payment receipt for the call.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "model": {
   "type": "string",
   "description": "Model id from GET /v1/models; xfuel/auto routes automatically"
  },
  "stream": {
   "type": "boolean"
  },
  "messages": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "role",
     "content"
    ],
    "properties": {
     "role": {
      "enum": [
       "system",
       "user",
       "assistant"
      ],
      "type": "string"
     },
     "content": {
      "type": "string"
     }
    }
   },
   "description": "OpenAI-style chat messages array"
  },
  "max_tokens": {
   "type": "integer",
   "description": "Output token budget"
  },
  "temperature": {
   "type": "number",
   "maximum": 2,
   "minimum": 0
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "id": "chatcmpl-abc123",
  "model": "xfuel/auto",
  "usage": {
   "total_tokens": 15,
   "prompt_tokens": 10,
   "completion_tokens": 5
  },
  "xfuel": {
   "verify_url": "https://api.xfuel.app/receipt/xfuel-abc123"
  },
  "object": "chat.completion",
  "choices": [
   {
    "index": 0,
    "message": {
     "role": "assistant",
     "content": "Hello!"
    },
    "finish_reason": "stop"
   }
  ],
  "created": 1700000000
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/chit402-a2a-message-paid-llm-inference-with-usdc-receipts-871ac5ed/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.chit402.com](https://www.zero.xyz/host/api.chit402.com/llms.txt)