# Agent to Agent payments (a402)

### What is a402?

**a402** is the open payment protocol behind **Beep Pay**. a402 stands for `agent 402: payment required`\
It extends the original HTTP `402: Payment Required` status code into a **verifiable, on-chain payment layer** that lets *agents* pay and unlock digital resources autonomously — no human checkout, no custodians, no intermediaries.

At its core, a402 defines how **clients (agents)**, **facilitators**, and **merchants** interact to perform atomic, yield-aware USDC transfers tied to digital actions like API calls, model inference, file delivery, or app access.

The result: **instant, trustless machine-to-machine payments** — stable, programmable, and cryptographically verifiable.

#### 💡 The Idea

HTTP 402 has existed for decades as a reserved response code for “Payment Required,” but until now it had no implementation.\
a402 revives that concept by turning **HTTP requests into programmable payment flows** using stablecoins like **USDC**.

That means any `GET`, `POST`, or `RUN` request can include a verified, on-chain payment — allowing agents and apps to pay as part of the same network call.

#### ⚙️ How It Works

1. **Client (Agent)** requests access to a protected resource (e.g., API, AI endpoint, dataset).
2. **Server (Merchant)** responds with:

   ```javascript
   HTTP 402 Payment Required
   Payment-Request: <encoded a402 payload>
   ```
3. **Client** executes the stablecoin transfer and sends back a **payment receipt**.
4. **Server or Facilitator** verifies the receipt on-chain.
5. Once verified, access is **granted instantly**.

Every transaction is **stateless**, **verifiable**, and **non-custodial** — native to the web stack.

#### 💸 Why It Matters

a402 makes payments a **first-class citizen of the web**.\
Instead of bolting on legacy payment SDKs or redirect flows, it embeds **money movement directly into HTTP**.

This enables:

* **Pay-per-call APIs** (monetize inference, data, compute)
* **Pay-per-second** streaming for media or model usage
* **Agent-to-agent commerce** for autonomous systems
* **Instant microtransactions** with no intermediaries or credit rails

In short, a402 bridges **the internet and the financial layer** — seamlessly, natively, and globally.

#### 🔐 Key Properties

* **Stablecoin-native:** built around on-chain USDC transfers
* **Instant settlement:** sub-second confirmation (Sui)
* **Verifiable receipts:** every payment has a cryptographic proof
* **Non-custodial:** sender and receiver control their own vaults
* **Composable:** works with existing web standards (HTTP headers, status codes)

#### How does a402 compare to x402 or L402?

* L402 (Lightning): macaroon‑based auth + satoshi payments; great for BTC, requires Lightning infra.
* x402 (Coinbase): strong push for EVM chains, lacks identity.
* a402: built‑in identity/authorization, off‑chain session channels for bursty micro‑flows.

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