Payment Guide for AI Agents

1. Fast path

1. Do not prepay. Make the intended API request first. The 402 response gives the exact amount, recipient, asset and network for that endpoint.
2. Choose one accept block. Base L2 is EVM-compatible; Solana has the lower per-call price.
3. Transfer exact atomic units of canonical USDC. USDC has six decimals: 5000 = $0.005.
4. Retry the original method, URL and body once with its confirmed transaction hash. One hash redeems one call only.

Copy# Probe normally — first 4 qualifying calls are free
curl -i -X POST https://x402.agentsea.vn/v1/scrape/clean-markdown \
  -H 'Content-Type: application/json' \
  -d '{"url":"https://example.com"}'

# After trial: HTTP/1.1 402 Payment Required
# Decode the payment terms; choose ONE accepts[] entry.
python3 -c 'import base64,json,sys; print(json.dumps(json.loads(base64.b64decode(sys.stdin.read().strip())),indent=2))' \
  <<< "$PAYMENT_REQUIRED_BASE64"

2. Live recipient terms

3. Base L2 payment — automated agent example

Use this when the agent owns an EVM wallet and can make an ERC-20 transfer. It is direct, independent of a payment intermediary, and matches the live verifier.

Copy// Node 20+. npm i ethers
// export EVM_PRIVATE_KEY=0x...  # keep this only in your secret manager
import { ethers } from "ethers";

const endpoint = "https://x402.agentsea.vn/v1/scrape/clean-markdown";
const body = { url: "https://example.com" };
const rpc = new ethers.JsonRpcProvider("https://mainnet.base.org");
const signer = new ethers.Wallet(process.env.EVM_PRIVATE_KEY, rpc);
const usdc = new ethers.Contract(
  "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  ["function transfer(address to,uint256 value) returns (bool)"], signer
);

// 1) Probe — 200 means free trial; 402 carries dynamic terms.
let res = await fetch(endpoint, {method:"POST",headers:{"Content-Type":"application/json"},body:JSON.stringify(body)});
if (res.status === 200) console.log(await res.json());
else if (res.status === 402) {
  const p = JSON.parse(Buffer.from(res.headers.get("payment-required"), "base64").toString("utf8"));
  const term = p.accepts.find(x => x.network === "eip155:8453");
  if (!term || term.asset.toLowerCase() !== "0x833589fcd6edb6e08f4c7c32d4f71b54bdA02913") throw Error("Unexpected payment terms");

  // 2) Send exact USDC and await confirmation.
  const tx = await usdc.transfer(term.payTo, BigInt(term.amount));
  await tx.wait(1);

  // 3) Resubmit the same resource exactly once with proof.
  res = await fetch(endpoint, {method:"POST",headers:{"Content-Type":"application/json","X-PAYMENT":JSON.stringify({txHash:tx.hash,network:term.network})},body:JSON.stringify(body)});
  console.log(res.status, await res.json());
} else throw Error(`Unexpected HTTP ${res.status}`);

4. Solana payment — agent contract

For a Solana-capable agent, select the accepts[] block whose network starts with solana:, transfer its exact amount of the stated USDC mint to payTo, wait for finalized confirmation, then resubmit this payload:

CopyPOST https://x402.agentsea.vn/v1/guard/prompt-injection-check
Content-Type: application/json
X-PAYMENT: {"txHash":"<finalized Solana signature>","network":"solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp"}

{"text":"content to inspect"}

5. HTTP contract an agent must follow

Challenge

CopyHTTP/1.1 402 Payment Required
Payment-Required: <base64 JSON envelope>
X-PAYMENT-NETWORKS: eip155:8453,solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp
X-PAYMENT-AMOUNT: 5000
X-PAYMENT-BASE-RECIPIENT: 0x2965570f64c9c2FB5b9c09bf36529A6438696969
X-PAYMENT-SOLANA-RECIPIENT: TediZmm6dE7Q1pU6FjwCs9uRT4UVx8uPWk8SDCSHkaF

Payment proof accepted now

CopyX-PAYMENT: {"txHash":"0x<Base transfer transaction hash>","network":"eip155:8453"}
# OR
X-PAYMENT: {"txHash":"<Solana transfer signature>","network":"solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp"}

Rules

• Amount must be at least the requested amount in the selected network's accepts[] term.
• Recipient and asset must exactly match the selected term.
• One confirmed transaction hash can redeem one request only. Replays return HTTP 402.
• Paid calls bypass the 20/hour unpaid IP rate limit.
• Never pay more than the selected amount; use per-call spend limits in the agent wallet.

6. MCP discovery

Agents can inspect tools and JSON schemas through Remote MCP before they pay:

Copy# Discover all tools
curl -s -X POST https://x402.agentsea.vn/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}'

# Machine-readable discovery documents
https://x402.agentsea.vn/.well-known/agent-card
https://x402.agentsea.vn/.well-known/x402
https://x402.agentsea.vn/openapi.json
https://x402.agentsea.vn/SKILL.md

7. Protocol status — do not assume unsupported paths

8. Error handling