> ## Documentation Index
> Fetch the complete documentation index at: https://docs.usecontra.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# x402 (Agentic Pay-per-Call)

> The account-less front door. Wallet = tenant. Pay USDC per call. No signup.

x402 is the **agentic-native entrypoint** — an autonomous agent with a wallet can use Contra **without ever registering**, paying USDC per call. The wallet that pays *is* the tenant.

## The handshake

```http theme={null}
POST /v1/sessions
→ HTTP 402 Payment Required
{
  "asset":   "USDC",
  "network": "base",
  "maxAmount": "100000",        // 0.10 USDC
  "payTo":   "0xContraMerchant",
  "nonce":   "0x…",
  "resource": "create_verification"
}

# Agent's wallet signs an EIP-3009 transferWithAuthorization
# Retries with X-Payment header

POST /v1/sessions     (with X-Payment)
→ 200 OK · ContraToken
```

## How billing aligns with cost

* **Hold at start** (no charge yet) → Smile may incur cost.
* **Settle at decision** (charge only if a verdict was produced) → fair to both sides.
* **Status reads are free** (`GET /v1/sessions/:id`).
* **Compliance lookups are free** (`GET /v1/compliance/:address` — on-chain read mirror).

## When to use x402

* You're building **for an autonomous agent**, not a human dev.
* You want **no signup, no key, just a wallet**.
* You're calling per-transaction and want **strict cost↔value alignment**.

If instead you're a company onboarding many users, use the [multi-tenant SDK](/integrate/api-keys) with a normal `x-api-key`.