Skip to main content

​
Payment Flow Guide

⚠️ Mainnet Only — All payments use Solana mainnet USDC. There is no devnet or testnet mode.
ASG Agent Cloud uses a 2-step payment flow based on the HTTP 402 Payment Required standard. This guide shows you exactly how it works with copy-paste curl examples.

​
How It Works

​
Step 1: Request a Quote

Call any billable tool without a payment proof. The gateway returns a 402 Payment Required response with a quote and payment instructions. 
curl -X POST https://agent.asgcompute.com/v1/mcp/tools/call \
  -H "Authorization: Bearer sk-agent-YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "tool": "inference_chat",
    "params": {
      "model": "google/gemini-2.0-flash-001",
      "messages": [{"role": "user", "content": "Hello"}]
    }
  }'

​
402 Response

{
  "code": "PAYMENT_REQUIRED",
  "message": "Payment required to execute tool",
  "quote": {
    "quote_id": "qt_abc123",
    "tool": "inference_chat",
    "price_usdc_microusd": 10000,
    "price_display": "$0.01",
    "ttl_seconds": 300,
    "expires_at": "2026-02-08T12:05:00Z"
  },
  "payment_instructions": {
    "network": "solana-mainnet",
    "asset": "USDC",
    "pay_to": "<treasury_ata>",
    "usdc_mint": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
    "memo_format": "step_id:quote_id:nonce",
    "methods": ["x402_header", "body_payment_proof"]
  },
  "step_id": "step_xyz"
}
Save the quote_id, step_id, pay_to, and usdc_mint from this response — you’ll need them to build the payment.

​
Step 2: Pay and Retry

After sending USDC on Solana mainnet, retry the same tool call with your payment proof attached. ASG supports two methods:

​
Method A: Body payment_proof (Primary)

Include the payment proof directly in the request body: 
curl -X POST https://agent.asgcompute.com/v1/mcp/tools/call \
  -H "Authorization: Bearer sk-agent-YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "tool": "inference_chat",
    "params": {
      "model": "google/gemini-2.0-flash-001",
      "messages": [{"role": "user", "content": "Hello"}]
    },
    "payment_proof": {
      "tx_ref": "YOUR_SOLANA_TX_SIGNATURE",
      "amount_usdc": "0.01",
      "memo": "step_xyz:qt_abc123:1",
      "network": "solana-mainnet"
    },
    "idempotency_key": "unique-key-per-request"
  }'

​
Method B: X-Payment Header (x402 Standard)

Encode the payment proof as base64 JSON and pass it in the X-Payment header: 
# Encode payment proof as base64 JSON
PAYMENT=$(echo -n '{"tx":"YOUR_SOLANA_TX_SIGNATURE","quote_id":"qt_abc123"}' | base64)

curl -X POST https://agent.asgcompute.com/v1/mcp/tools/call \
  -H "Authorization: Bearer sk-agent-YOUR_KEY" \
  -H "X-Payment: $PAYMENT" \
  -H "Content-Type: application/json" \
  -d '{
    "tool": "inference_chat",
    "params": {
      "model": "google/gemini-2.0-flash-001",
      "messages": [{"role": "user", "content": "Hello"}]
    },
    "idempotency_key": "unique-key"
  }'

​
Success Response (200)

{
  "ok": true,
  "result": {
    "type": "text",
    "content": "Hello! How can I help you today?"
  },
  "receipt": {
    "receipt_id": "rcpt_123",
    "debited_usdc_microusd": 10000
  }
}

​
Field Reference

FieldDescriptionExample
tx_refSolana transaction signature (base58)5x7Hk...
amount_usdcAmount in USDC (string)"0.01"
memoFormat: step_id:quote_id:nonce"step_xyz:qt_abc123:1"
networkMust be solana-mainnet"solana-mainnet"
idempotency_keyUnique per request (prevents double-billing)"550e8400-..."
quote_idQuote ID from 402 response"qt_abc123"

​
Idempotency

Always include an idempotency_key with your payment proof. If a request is retried with the same key, ASG returns the cached result without charging again. This prevents double-billing on network errors.

​
Error Handling

Error CodeMeaningAction
PAYMENT_REQUIREDNo payment attachedGet quote, pay, retry
QUOTE_EXPIREDQuote TTL exceededRequest a new quote
INVALID_PAYMENTPayment verification failedCheck tx_ref and amount
RATE_LIMITEDToo many requestsBack off and retry

​
Next Steps

Tool Availability

See which tools are currently active

Billing Overview

Understand the billing model

SDK Examples

TypeScript examples with payment flow

Payment Contract

Full technical payment contract reference