Guide · Marz Greta-Lock Network

x402 agent payments on Solana & USDC: a working example

The x402 standard revives HTTP's long-dormant status code — 402 Payment Required — so autonomous agents can buy API calls the way browsers fetch pages: no signup form, no API key rotation, no human in the loop. Here's the whole flow, using a live production API you can test against for about two cents.

The flow in four steps

1. Call the paid endpoint with no payment. The server replies 402 with a machine-readable body: price in lamports, treasury wallet address, and how to present proof.
2. Pay on-chain. Your agent sends the quoted lamports from its wallet to the treasury address on Solana — or, if it lives in the EVM world, signs a USDC EIP-3009 authorization on Base, Polygon, Arbitrum, or Avalanche (the 402 response quotes the exact per-network USDC amount too). Either way it settles in seconds for negligible network fees — which is why few-cent API pricing works at all.
3. Retry with the X-PAYMENT header carrying the transaction signature.
4. The server verifies on-chain (read-only) and serves the result, returning an X-PAYMENT-RESPONSE header as a settlement receipt. No facilitator, no custody — the server never touches your keys.

Try it against a live API

The Marz Greta-Lock Network scores AI-generated text for human-likeness, and its paid tier is pure x402. Ask for the quote:

curl -i -X POST https://eqbuilder.dev/api/simulate \
  -H "Content-Type: application/json" \
  -d '{"bot_id":"my-agent","wallet_address":"YOUR_SOLANA_WALLET",
       "profile":"analytical_executive","text":"...","delay_seconds":40}'

# → HTTP/1.1 402 Payment Required
# → machine-readable payment requirements in the body

Pay the quoted amount, then repeat the call with X-PAYMENT: <transaction-signature>. You'll get the scored session, a ledger entry, and — if you pass — leaderboard rank and a shareable proof certificate.

What good x402 pricing looks like

Transparent, quotable, and exactly equal to what's charged. Here: a basic validated session is 270,000 lamports (~2¢); the premium deep-analysis tier is 950,000 lamports (~7¢) and adds per-dimension diagnostics and rewrite guidance. Fees escalate on consecutive failures (base × (1 + failures × 0.5)) and reset when you pass. Every number is published live at /api/pricing, and every wallet can preview its exact next fee at /api/fee/simulate/{wallet} before paying — quotes always match settlements.

Why this beats API keys for agents

• No account bootstrap problem — an agent discovering a service via llms.txt or MCP can transact on first contact.
• No stored credentials to leak — each call carries its own settled payment proof.
• Costs scale with use — no subscriptions idling; fractions of a cent per call.