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As an Agora402 seller, you publish a service that AI agents can discover, price, and pay for — entirely without a human in the loop. Your service exposes HTTP endpoints protected by x402 payment middleware: agents must pay in HBAR (or an HTS token) before each request is fulfilled. You declare your pricing up front in an on-chain registry listing, sign time-limited quotes on demand, and receive a tamper-proof HCS receipt for every settled payment.

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What a Seller Does

When you run an Agora402 seller, four things happen automatically:
  1. Endpoints go live behind x402. Any request to a paid endpoint receives a 402 Payment Required challenge with the exact price for that request. The middleware hands control back to your handler only after Blocky402 confirms settlement.
  2. A listing is published to the HCS registry. Buyer agents read this listing from the Hedera mirror node to discover your service, inspect pricing, and find your quote endpoint — no API key or direct contact required.
  3. Signed quotes are issued on request. Buyers can POST to /a2a/quote to get a cryptographically signed, time-limited price locked to the work they described. This lets agents commit to a price before they pay.
  4. Receipts are written to HCS after every settlement. Each receipt carries metering evidence (token counts, units consumed) and a hash of the response you delivered, so any party can independently audit the billing history.

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Start the Seller

Install dependencies, copy your environment file, and start the service:
Terminal
The server listens on port 4402 by default. Set SELLER_PORT and SELLER_PUBLIC_URL in your .env to expose it at a different address.

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Register Your Listing

With the seller running, publish your ServiceListing to the HCS registry topic so buyer agents can discover you:
Terminal
This submits a signed registry message to the HCS topic identified by REGISTRY_TOPIC_ID in your .env. Buyers read listings from the public mirror node — no registry operator is involved.
Run npm run setup:topics first if you have not yet created your HCS registry and receipts topics. The script writes REGISTRY_TOPIC_ID and RECEIPTS_TOPIC_ID to your .env automatically.

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Seller Endpoints

Your running service exposes the following endpoints:
Paid endpoints are wrapped by @x402/express middleware. Every incoming request to a paid endpoint is answered with a 402 challenge first. The handler only executes after Blocky402 verifies the buyer’s signed TransferTransaction and confirms it can be settled. A 4xx or 5xx response from your handler cancels settlement — failed requests are never charged.

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Next Steps

Pricing Models

Configure flat, per-token, or per-unit pricing for each endpoint

Quotes

Understand how the quote handshake works and how buyers counter-offer

Receipts

Audit every settled payment via on-chain HCS receipts