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A payment scheme defines how a payment is made on a specific blockchain. Schemes handle the chain-specific details: constructing transactions, signing them, and producing the proof that gets sent in the X-PAYMENT header.

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Scheme identification

Every payment is identified by a tuple of three values:
FieldExampleDescription
scheme"exact"The payment method
network"solana-devnet"The blockchain network
asset"USDC"The token being used
When a server returns payment requirements, the client matches against this tuple to find a compatible payment handler.

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Solana schemes

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SPL Token payments

The primary Solana scheme uses SPL token transfers for payments. The client signs a transaction transferring tokens from their wallet to the merchant’s address. 
import { xSolanaSettlement } from "@faremeter/info/solana"

const requirements = xSolanaSettlement({
  network: "devnet",
  payTo: "7xKXwxRPMo2sUAT5...",
  asset: "USDC",
  amount: "10000",
})
Supported assets: USDC (devnet, mainnet-beta).

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Native SOL

Faremeter also supports native SOL transfers for Solana payments.

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EVM schemes

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EIP-3009 gasless transfers

The EVM scheme uses EIP-3009 transferWithAuthorization for gasless USDC payments. The client signs an EIP-712 typed message authorizing the transfer. The facilitator submits the transaction on-chain and pays the gas fees. 
import { x402Exact } from "@faremeter/info/evm"

const requirements = x402Exact({
  network: "base-sepolia",
  asset: "USDC",
  amount: "10000",
  payTo: "0x1234...",
})
Supported networks: Base Sepolia, Base, Polygon, Skale Europa Testnet, Monad. The gasless design means clients never need native tokens for gas. The facilitator covers transaction costs.

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How schemes compose

Faremeter’s plugin architecture allows multiple schemes to coexist. A server can accept both Solana and EVM payments simultaneously: 
import { createMiddleware } from "@faremeter/middleware/express"
import { xSolanaSettlement } from "@faremeter/info/solana"
import { x402Exact } from "@faremeter/info/evm"

const middleware = await createMiddleware({
  facilitatorURL: "https://facilitator.corbits.dev",
  accepts: [
    xSolanaSettlement({ network: "devnet", payTo: "7xKX...", asset: "USDC", amount: "10000" }),
    x402Exact({ network: "base-sepolia", payTo: "0x1234...", asset: "USDC", amount: "10000" }),
  ],
})
The client selects the scheme it can fulfill based on its available wallets.

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Adding new schemes

New payment schemes can be added through the payment handler interface. See Extensions for community-contributed schemes.

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Further reading