💳Intermediate⏱ 45 min

x402 Payment Protocol Deep Dive

The x402 protocol extends HTTP with a 402 Payment Required flow. When a client hits a gated endpoint, the server returns a 402 with payment details. The client pays on-chain and retries with a receipt. This quest walks through the entire flow from scratch.

x402usdcpaymentsexpressbase-l2

Prerequisites:Your First Agent on Base

🏆

Ability to build and monetize any HTTP endpoint with x402 payments

Step 1: Understand the 402 handshake

A 402 response tells the client how much to pay, to which address, on which chain. The client uses `x402-fetch` or a compatible library to pay and retry.

Step 1 — json

// What a 402 response looks like
{
  "x402Version": 1,
  "accepts": [{
    "scheme": "exact",
    "network": "base-mainnet",
    "maxAmountRequired": "10000", // 0.01 USDC (6 decimals)
    "resource": "https://hub.d0xeddev.com/api/hub-data",
    "description": "Hub data feed",
    "mimeType": "application/json",
    "payTo": "0xYourPaymentAddress",
    "maxTimeoutSeconds": 300,
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "extra": { "name": "USDC", "version": "2" }
  }]
}

✓

Checkpoint

Can describe the 402 handshake in your own words

1 / 3