Your first payment
A worked end-to-end example with real on-chain data.
This is the exact code we ran to validate the live production endpoint.
The transaction below is on Solana devnet (so you can inspect it without
spending real USDC). Mainnet works identically — pass
network: "mainnet" to payAndInfer and the payment lands on Solana
mainnet instead.
Last verified workingreceipt 0d3a5b26↗
The full script
import { X402Agent } from "@vdm-nexus/x402";
// Throwaway demo keypair — replace with your own.
const agent = X402Agent.fromBase58(process.env.AGENT_SECRET!);
const reply = await agent.payAndInfer(
"https://nexus.vdmnexus.com/api/v1",
{
model: "openai/gpt-4o-mini",
messages: [
{
role: "user",
content:
"In one sentence, what's the point of a cryptographic receipt on an LLM call?",
},
],
}
);
console.log("Response:", reply.openai.choices[0].message.content);
console.log("Receipt:", reply.receipt);
console.log("Payment:", reply.payment);
console.log(
"Solscan:",
`https://solscan.io/tx/${reply.payment?.txSignature}?cluster=devnet`
);What the response looked like
Response: A cryptographic receipt on an LLM call serves to provide
verifiable proof of the transaction or interaction, ensuring data
integrity and authenticity while allowing for auditability and
accountability.
Receipt: {
agent_pubkey: 'FFcH3cdWFLy3i1zprtRWFY8D8P6QX6DQmcwwmABqP77U',
upstream: 'openrouter',
model: 'openai/gpt-4o-mini',
cost_usdc: 0.000025,
prompt_hash: '64914968651ba207c2dee425f15d8cacc671647227106ea149e06a959db40b52',
response_hash: '9861ad24639cea52d146ff3b64e003084ceeba5c2d3348791bfa6a9b753afb91',
timestamp: 1779210181044,
inference_id: '98dc7bb0-24a0-41f3-872c-9b4c4786c280',
payment: {
scheme: 'x402',
amount_usdc: 0.01,
tx_signature: 'rVTKk6XguuWKLpqt3mMNKSSBCTm5LLeAHJo4ckCc2f8yGmSgEyGCPR9va1EB23C8i71mJm7r34ecDo7V4pKxyrr',
network: 'solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1'
}
}Solscan link: tx rVTKk6X…
Total wall-clock time from intent to receipt: 4.9 seconds, almost all of it Solana confirmation.
Cost breakdown
- Charged to the agent: 0.01 USDC (the flat fee declared in the 402 challenge)
- Real OpenRouter cost: 0.000025 USDC (25 prompt tokens + 35 completion tokens at gpt-4o-mini rates)
- Difference: held as a positive ledger balance for the agent. The current flat-fee pricing model overshoots actual cost by ~400×; a token-priced refund model is on the roadmap.
Error cases worth handling
import {
X402PaymentRequiredError,
X402PaymentReplayError,
X402UpstreamError,
} from "@vdm-nexus/x402";
try {
await agent.payAndInfer(endpoint, opts);
} catch (e) {
if (e instanceof X402PaymentReplayError) {
// 409 — same tx_signature already credited. The agent's call was
// already paid for. Treat as success or surface to the operator.
} else if (e instanceof X402PaymentRequiredError) {
// 402 from a deeper check — payment was malformed or facilitator
// rejected it. Inspect e.detail.
} else if (e instanceof X402UpstreamError) {
// 502 or unexpected status. Inspect e.status and e.detail.
} else {
throw e;
}
}