# Synap Billing Top-Up via x402

> Synap Billing Top-Up via x402 is a paid API for AI agents from synap.linkrra.com, paid per call via x402, $1/call, status unknown (last checked 2026-10-23).

Tops up a Synap account balance by processing a $1 USDC micropayment via the x402 payment protocol, returning the updated credit balance.

## Facts

- Endpoint: POST https://synap.linkrra.com/api/billing/x402/topup?utm_source=zero.xyz
- Price: $1/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-23
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/synap-billing-top-up-via-x402-f3d0cbac
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_XkR1Ivx2OZYqj8-eftxMW

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 synap-billing-top-up-via-x402-f3d0cbac -d '<json body>'
```

Example prompt: Top up my Synap AI account balance with $1 USDC so I can keep running inference requests against the qwen3-coder-30b model.

## When to prefer this

Use this endpoint when an AI agent or automated pipeline needs to programmatically fund a Synap inference account using the x402 micropayment protocol (USDC on-chain). Prefer this over manual top-up flows when operating in an agentic context where credits must be replenished automatically without human intervention. This is specifically suited for x402-compatible payment flows and not for traditional credit card or fiat billing.

## Known failure modes

- Payment failure: insufficient USDC funds in the paying wallet returns an error
- Invalid x402 payment header: malformed or missing payment proof causes rejection
- Network error: timeout or connectivity issue during payment processing
- Duplicate payment: submitting the same payment nonce twice may be rejected
- Account not found: mismatched credentials result in top-up not being applied

## How this service works

AI powered by the people, for the people. OpenAI-compatible inference API with zero data retention — qwen3-coder-30b at $0.0675/1M in, $0.27/1M out. Contribute your GPU, earn credits.

## Output

Returns a JSON object with 'ok' (boolean success flag), 'balance' (integer representing the updated account balance in micro-credits), and 'credits' (integer equal to balance, confirming the new credit total after the top-up).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "required": [
  "input",
  "output"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object"
    },
    "type": {
     "type": "string"
    },
    "method": {
     "type": "string"
    },
    "bodyType": {
     "type": "string"
    }
   }
  },
  "output": {
   "type": "object",
   "required": [
    "type",
    "example"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "balance": 4399472,
  "credits": 4399472
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/synap-billing-top-up-via-x402-f3d0cbac/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from synap.linkrra.com](https://www.zero.xyz/host/synap.linkrra.com/llms.txt)