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

# X402

x402 is a pay-per-use payment protocol that ScaleX agents use to gate their trading services. Before an agent executes a strategy for a user, it verifies that a valid x402 payment has been made, enabling agents to monetize their strategies on a per-trade or per-session basis, entirely on-chain.

## What Is x402?

x402 is a lightweight HTTP-native payment standard (inspired by the HTTP 402 "Payment Required" status code) adapted for on-chain use. In ScaleX, it acts as a **payment gate at the agent execution layer**, agents check for a valid payment receipt before processing any user request.

This allows agent developers to:

* Charge users per trade, per session, or per strategy activation
* Enforce payment without a centralized billing system
* Accept payments in any supported token (USDC, ETH, etc.)

## How It Works in ScaleX

```
User wants Agent to trade for them
  │
  ▼
User sends x402 payment to Agent's payment address
  │
  ▼
Agent verifies payment receipt on-chain
  │
  ▼
AgentRouter.execute*() is called, trade proceeds
  │
  ▼
Payment recorded; agent earns revenue
```

If no valid payment exists, the agent rejects the request before it ever reaches the `AgentRouter`. This keeps payment logic cleanly separated from trading logic.

## Payment Models

Agents can configure different payment structures depending on their strategy:

| Model             | Description                                              | Best For                         |
| ----------------- | -------------------------------------------------------- | -------------------------------- |
| **Pay-per-trade** | User pays a small fee for each order placed              | Casual users, one-off strategies |
| **Session-based** | User pays once to unlock a time window (e.g., 24h)       | Active traders                   |
| **Subscription**  | Recurring off-chain payment unlocks on-chain permissions | Long-term managed portfolios     |
| **Volume-tiered** | Fee decreases as trading volume increases                | High-frequency traders           |

## Integration with AgentRouter

The `AgentRouter` supports x402 verification natively. Before dispatching a trade, it checks the payment state for the calling agent:

```solidity theme={null}
function executeOrder(
  address userAddress,
  uint256 strategyAgentId,
  OrderParams calldata params
) external {
  // Standard authorization checks
  require(msg.sender == ownerOf(strategyAgentId), "Not agent owner");
  require(authorizedStrategyAgents[userAddress][strategyAgentId], "Not authorized");

  // x402 payment gate
  require(
    _x402Gateway.isPaymentValid(strategyAgentId, userAddress),
    "x402: payment required"
  );

  // Execute trade
  _dispatchOrder(userAddress, params);
}
```

## Payment Flow Example

**Scenario:** A user wants a trading agent to manage their BTC/USDC limit orders for 24 hours.

1. User sends 5 USDC to the agent's x402 payment address
2. The x402 gateway records a 24-hour valid payment for `(agentId, userAddress)`
3. For the next 24 hours, every `AgentRouter.execute*()` call passes the payment check
4. After expiry, the agent stops executing until the user pays again

## Benefits

### For Agent Developers

* **Monetize strategies** without building a billing system
* **Trustless revenue**: payments are on-chain, no chargebacks
* **Flexible pricing**: set any fee model that suits the strategy
* **Composable**: x402 receipts can be verified by any contract

### For Users

* **Pay only for what you use**: no upfront lock-in
* **Transparent pricing**: fee amounts are visible on-chain
* **Control**: stop paying to immediately halt agent execution
* **No custody risk**: payment does not give agents additional fund access beyond their policy

## Security Considerations

* **Payment ≠ fund access**: an x402 payment only unlocks execution rights; the user's policy still governs what the agent can do with funds
* **Non-transferable receipts**: a payment receipt is bound to a specific `(agentId, userAddress)` pair and cannot be reused
* **Expiry enforcement**: time-based payments are enforced at the contract level, not by the agent

x402 completes the ScaleX agent monetization stack. Agents can earn yield on deposits, charge for strategies via x402, and compete for leaderboard rewards, all within a single composable on-chain system.