Swap your API key for a sk_test_ key - that alone puts you on Base Sepolia. Fund the agent's wallet from the public Base Sepolia USDC faucet, make a real test payment with payments.create (test funds, no real money), and tunnel your local webhook through ngrok. The response shapes match live, so a flow that passes in test passes in production. Exercise the failure paths, not just the happy one.

Switch to a test key.

A sk_test_ key transacts on Base Sepolia; a sk_live_ key transacts on Base mainnet. The prefix picks the network - there is no separate network env var, and a test key cannot move mainnet funds. So all you change for a dev environment is the key (and the test webhook secret).

# .env.development
# A sk_test_ key picks Base Sepolia automatically - there is no network env var.
BLOCKCHAIN0X_API_KEY=sk_test_01J9...
BLOCKCHAIN0X_WEBHOOK_SECRET=...   # the test webhook's secret, from the dashboard

Make a real test payment.

With the wallet funded, call payments.create on your sk_test_ key. It is a real transfer on Base Sepolia using test funds, and it fires the payment.received webhook exactly as mainnet would - so you exercise the actual code path, not a simulation. Watch the event land at your tunnelled handler.

// On a sk_test_ key this is a REAL transfer on Base Sepolia (test funds, no
// real money). It fires the payment.received webhook just like mainnet does.
const tx = await client.payments.create({
  agentId: "agt_123",
  to: "0xRecipientOnSepolia",
  amountWei: "10000", // 0.01 USDC
});

console.log(tx); // watch payment.received arrive at your webhook

tx = client.payments.create(body={
    "agentId": "agt_123",
    "to": "0xRecipientOnSepolia",
    "amountWei": "10000",  # 0.01 USDC
})

print(tx)  # watch payment.received arrive at your webhook

Three scenarios to exercise at minimum: a payment that lands (the happy path, payment.received), a payment that never lands (point the webhook at a dead URL and confirm your reconcile sweep catches the stuck job - the path most teams ignore), and a webhook retry (force a 500 the first time and 200 the second, then verify your idempotency skipped the duplicate work).

Fail fast on misconfigured keys.

The single most common production incident around test/live keys is silent: a deploy lands with a test key, no payments come through, alerts only fire after the next business day. Block this at boot: refuse to start if the env and the key prefix do not match.

// Fail fast if test/live get mixed up.
const apiKey = process.env.BLOCKCHAIN0X_API_KEY!;
const env = process.env.NODE_ENV;

if (env === "production" && apiKey.startsWith("sk_test_")) {
  throw new Error("Test key in production environment - aborting boot.");
}
if (env !== "production" && apiKey.startsWith("sk_live_")) {
  throw new Error("Live key in non-production environment - aborting boot.");
}

import os, sys

api_key = os.environ["BLOCKCHAIN0X_API_KEY"]
env = os.environ.get("ENV", "development")

if env == "production" and api_key.startswith("sk_test_"):
    sys.exit("Test key in production environment - aborting boot.")
if env != "production" and api_key.startswith("sk_live_"):
    sys.exit("Live key in non-production environment - aborting boot.")

Once the test loop is in your dev cycle.

With a healthy test loop in place, the remaining work is mostly hardening: dependable webhook handling under load, a final security checklist, and migrations from any prior payment provider you may be running alongside.

Full reference at docs.blockchain0x.com. Testnet details: Base chain glossary. Product surface: Payment API.