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

# Exact and Upto

> Per-call payment schemes — no pre-funding needed.

The `exact` and `upto` schemes let you pay per request without pre-funding a channel. Each call results in an on-chain transfer.

## Exact

Fixed-price payments. The server advertises a price, you sign for that exact amount, and the facilitator settles an on-chain transfer.

```typescript theme={null}
import ComposeSDK, { createPrivateKeyX402EvmWallet } from "@compose-market/sdk";

const { x402Signer } = createPrivateKeyX402EvmWallet({
  privateKey: "0xYourPrivateKey",
  schemes: ["exact"],
});

const sdk = new ComposeSDK({
  userAddress: "0xYourWalletAddress",
  chainId: 43113,
});
```

Use `exact` for:

* One-shot API calls
* Fixed-price resources (file downloads, gated pages)
* When you don't want to pre-fund a channel

The signer does not need an RPC URL for `exact` — no on-chain state to read.

## Upto

Usage-based payments. The server advertises a maximum price, you sign a Permit2 authorization for that maximum, and the server charges the actual usage after processing.

```typescript theme={null}
const { x402Signer } = createPrivateKeyX402EvmWallet({
  privateKey: "0xYourPrivateKey",
  rpcUrl: "https://avax-fuji.g.alchemy.com/v2/YourRpcKey",
  schemes: ["upto"],
});
```

Use `upto` for:

* LLM token billing (charge for actual tokens used)
* Compute-time billing
* Dynamic data queries where the cost varies

The settled amount is always less than or equal to the signed maximum. The server uses settlement overrides to charge the actual amount:

```typescript theme={null}
// The SDK receives the final amount in the receipt
const result = await stream.next();
console.log(result.receipt.bills[0].total); // actual amount charged
```

## Register multiple schemes

You can register all three schemes at once — the SDK picks the right one based on what the server advertises:

```typescript theme={null}
const { x402Signer } = createPrivateKeyX402EvmWallet({
  privateKey: "0xYourPrivateKey",
  rpcUrl: "https://avax-fuji.g.alchemy.com/v2/YourRpcKey",
  schemes: ["batch-settlement", "upto", "exact"],
});
```

## Transfer methods

The EVM implementation supports two transfer methods:

| Method    | Description                                                      |
| --------- | ---------------------------------------------------------------- |
| `eip3009` | Uses token-native `transferWithAuthorization`. Default for USDC. |
| `permit2` | Uses Uniswap Permit2 plus an x402 proxy. Supports any ERC-20.    |

The SDK automatically selects the right method based on the token's capabilities.