How do I test x402 payments on Base Sepolia before mainnet?

1. Point your route at Base Sepolia

This is the route config from the x402 seller quickstart (Express). A dollar price like "$0.001" is paid in the network’s default USDC.

const server = new x402ResourceServer(
  new HTTPFacilitatorClient({ url: "https://x402.org/facilitator" })
).register("eip155:84532", new ExactEvmScheme());

app.use(paymentMiddleware({
  "GET /weather": {
    accepts: [{ scheme: "exact", price: "$0.001", network: "eip155:84532", payTo }],
    description: "Get current weather data",
    mimeType: "application/json",
  },
}, server));

On 14 Oct 2026 the facilitator’s /supported list showed exact, upto and batch-settlement on eip155:84532, and no eip155:8453.

2. Get test funds

• USDC: Circle’s faucet gives 20 testnet USDC per address, per chain, every 2 hours, with no account. Choose Base Sepolia.
• Token address: Base Sepolia USDC is 0x036CbD53842c5426634e7929541eC2318f3dCF7e (Circle’s address list). Only needed if you set the asset yourself instead of a dollar price.
• ETH: the CDP faucet dispenses Base Sepolia ETH, which a wallet needs to send its own transactions on the testnet.

3. Check the 402 before you pay

Paste your URL into the free x402 endpoint checker. On Base Sepolia it shows a warning, not a failure, because the network is a testnet. It fails the check if the USDC asset belongs to a different network from the one you declared, which catches a mainnet address left in a testnet config (or the reverse).

Then pay it with an x402 client, following the buyer quickstart. By default its client caps each payment at $1, so keep test prices small.

4. Switch to mainnet

The CDP seller quickstart (its prerequisites: a CDP API key, a payTo address and Node 22) says to confirm each payTo can receive on mainnet, and to swap any testnet asset address for its mainnet one. For the facilitator choice, see which facilitator works on Base mainnet and what each one costs (or the cost calculator).

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FAQ

Sources, checked 2026-10-14: x402 seller quickstart, x402.org /supported, Circle faucet, Circle USDC addresses, CDP seller quickstart, CDP faucet, x402 buyer quickstart.