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The x402 protocol is an HTTP-based payment standard that enables seamless micropayments on the web. It extends the HTTP 402 Payment Required status code to create a standardized payment negotiation flow.

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What is x402?

x402 solves the problem of web monetization by providing a standard way for clients and servers to negotiate and complete payments automatically, without manual intervention.

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Key Benefits

  • Automatic Payment Negotiation - No manual payment flows
  • Multi-Chain Support - Works with Base, Solana, and other chains
  • Standard HTTP Flow - Uses familiar HTTP patterns
  • Proof of Payment - Cryptographic verification of transactions
  • Developer Friendly - Simple integration with existing tools

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How x402 Works

The x402 protocol follows a simple 4-step flow:

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1. Initial Request

Your application makes a standard HTTP request to a payment-required endpoint: 
POST /payments/x/pay
{
  "amount": 0.01,
  "currency": "USDC",
  "receiver": "username"
}

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2. Payment Challenge (402 Response)

The server responds with 402 Payment Required and includes payment details in the response headers: 
HTTP/1.1 402 Payment Required
x-payment-request: <encoded-payment-requirements>
The payment request contains:
  • Payment amount and currency
  • Recipient address
  • Blockchain network
  • Transaction details

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3. Payment Execution

Your x402 client automatically:
  1. Decodes the payment requirements
  2. Creates and signs a blockchain transaction
  3. Submits the transaction to the network
  4. Waits for confirmation

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4. Retry with Proof

After payment confirmation, the client retries the original request with proof of payment: 
POST /payments/x/pay
x-payment-response: <encoded-payment-proof>

{
  "amount": 0.01,
  "currency": "USDC",
  "receiver": "username"
}
The server verifies the payment and returns success: 
{
  "code": 200,
  "msg": "0.01 USDC sent successfully",
  "data": {
    "txn_id": "...",
    "amount": 0.01,
    "receipt": "https://snack.money/x/username?txn=..."
  }
}

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Implementation Options

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Using x402 Clients

The easiest way to integrate x402 is using a pre-built client library: x402-axios (Recommended for most applications) 
npm install x402-axios
x402-fetch (For minimal dependencies) 
npm install x402-fetch
See our SDK Examples for implementation guides.

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Using the CLI

For command-line usage, use the Snack Money CLI: 
npx snackmoney send x/username 0.01
Learn more in the CLI documentation.

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Supported Networks

Snack Money’s x402 implementation supports:
  • Base (EVM) - USDC payments on Base mainnet
  • Solana (SVM) - USDC payments on Solana mainnet

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Security

x402 provides strong security guarantees:
  • Cryptographic Proofs - All payments are verified on-chain
  • No Custody - You maintain control of your private keys
  • Transparent - All transactions are publicly verifiable
  • Standard Protocol - Open specification, no vendor lock-in

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