🪙 Pay any iUSD-paywalled API with one fetch — payment-skill × Initia × x402

An AI agent hit an Initia paywall, got HTTP 402, the skill bridged USDC → iUSD via Skip:Go, signed a Cosmos MsgSend on initiation-2, paid 0.5 iUSD, walked off with the data — one fetchWithPayment(url) call, zero humans, ~30 seconds.

SDK = https://www.npmjs.com/package/n-payment

The agentic-payment thesis on Cosmos rails — same x402 muscle memory, but on a stablecoin (iUSD) whose yield rebates to the ecosystem instead of the issuer. Here’s the playbook. 🎯

---

🎯 What “x402 on Initia” actually means

x402 on EVM is EIP-3009 transferWithAuthorization. Cosmos has no EIP-3009, so the agent signs a plain bank-module MsgSend instead. The skill calls this scheme cosmos-msgsend, and the dance is identical:

• 📡 Hit URL → server returns HTTP 402 with a cosmos-msgsend challenge

• ✍️ Agent signs MsgSend(amount=0.5 iUSD, denom=ibc/…, to=payTo) on initiation-2

• ⛓️ Tx broadcasts to Initia REST → block included → tx hash returned

• 🔁 Agent retries the URL with the tx-hash header → 200 OK + payload

The kicker: if the agent has no iUSD yet, the same tool bridges USDC from any EVM source via Skip:Go before signing. One pay_url call, no human approving anything mid-flow.

---

⚡ The Recipe (5 steps)

1️⃣ Install the skill + set 3 env vars

# One-shot — detects your AI host (Claude Code / Kiro / Cursor / Gemini / …)
npx -y github:phamdat721101/payment-skill

# Required for any signing path
export INITIA_MNEMONIC="word1 word2 … word12"          # BIP-39, 12 or 24 words
export INITIA_IUSD_DENOM_TESTNET="ibc/<DENOM_HASH>"    # iUSD denom on initiation-2

• 🔑 INITIA_MNEMONIC derives the agent’s init1… bech32 address — never echoed, never written outside ~/.n-payment/

• 🪪 INITIA_IUSD_DENOM_TESTNET is mandatory — iUSD is an IBC denom, the hash differs testnet vs mainnet (use INITIA_IUSD_DENOM_MAINNET for interwoven-1)

• 📦 Optional peer deps (lazy-loaded on first signing call): npm i @cosmjs/proto-signing @cosmjs/stargate @skip-go/client

• 💧 Faucets: uinit gas at faucet.testnet.initia.xyz · Base Sepolia USDC at faucet.circle.com

2️⃣ quote — corridor selector + Skip API preview (no signing, no tx)

n-payment-skill tools call iusd_bridge '{
  "action": "quote",
  "amount_iusd": "0.5",
  "source_chain": "base-sepolia",
  "dest_chain": "initia-testnet"
}'

• 🧭 Returns the chosen corridor (skip-api on testnet · layerzero-ausd-oft or wormhole-ntt on mainnet) + your current iUSD / USDC holdings

• 💸 Pure read — no signer touched, no gas burned

• 🧪 Default route: base-sepolia USDC → initia-testnet iUSD (testnet-first by design)

3️⃣ balance — confirm iUSD + native gas

n-payment-skill tools call iusd_bridge '{
  "action": "balance",
  "dest_chain": "initia-testnet"
}'
# {
#   "address": "init1<INITIA_ADDR>",
#   "iusd": "0.000000",
#   "native_init": "0.250000",
#   "denom": "ibc/<DENOM_HASH>"
# }

• 🏷️ Reads iUSD (6 decimals) and uinit (the gas token) in one call

• 👀 Pass address to inspect any other Initia bech32 address (read-only, no mnemonic needed)

4️⃣ execute — bridge USDC → iUSD (dry-run first, then real)

# Dry-run: validate caps + corridor without sending tx
n-payment-skill tools call iusd_bridge '{
  "action": "execute",
  "amount_iusd": "0.5",
  "source_chain": "base-sepolia",
  "dest_chain": "initia-testnet",
  "dry_run": true
}'

# Real: signs USDC source leg + Cosmos receive leg via Skip API
n-payment-skill tools call iusd_bridge '{
  "action": "execute",
  "amount_iusd": "0.5",
  "source_chain": "base-sepolia",
  "dest_chain": "initia-testnet"
}'
# {
#   "corridor": "skip-api",
#   "tx_hashes": ["<EVM_TX_HASH>", "<INITIA_TX_HASH>"],
#   "iusd_landed": "0.500000",
#   "duration_ms": 28411,
#   "idempotency_key": "default-initia-testnet-0.5-1717…"
# }

• 🛡️ Conservative caps: IUSD_MAX_PER_TRANSFER=50 / IUSD_MAX_PER_DAY=200 (env-overridable)

• 🔁 idempotency_key auto-generated — replay safety baked in

• ⏱️ timeout_ms defaults to 600s; bump on slow IBC days

5️⃣ pay_url — call any iUSD-paywalled endpoint (auto-bridge if short)

import { createPaymentClient } from 'n-payment';

const client = createPaymentClient({
  chains: ['base-sepolia', 'initia-testnet'],
  ows: { wallet: 'default', privateKey: process.env.BUYER_KEY },
  initia: { network: 'testnet', mnemonic: process.env.INITIA_MNEMONIC! },
});

// One call — handles 402 cosmos-msgsend, auto-bridges USDC→iUSD if iUSD short
const res = await client.fetchWithPayment(
  'https://your-iusd-paywall.example/agent-api/decisions?limit=5',
);
console.log(await res.json());

• 🚦 If iUSD balance < maxAmountRequired → orchestrator quietly bridges, then signs the MsgSend

• 🧾 Returns { status, body, chain } — same shape as every other pay-style tool in the skill

• 🤖 From an MCP host (Kiro / Claude Code / Cursor): just say “pay this iUSD URL” — the skill picks iusd_bridge automatically

---

🧠 What’s under the hood

• 📦 IusdBridgeOrchestrator (n-payment v0.23) — picks the corridor, wires Skip API signers, enforces caps

• 🧭 selectIusdCorridor ranks skip-api / layerzero-ausd-oft / wormhole-ntt against holdings + chain health

• 🪪 InitiaClient soft-loads @cosmjs/*, builds the bech32 signer from your mnemonic, broadcasts via Initia REST

• 🛡️ guardMainnet runs before any interwoven-1 send — flip n-payment-skill config set testnetMode false to opt in

---

🚀 Why this matters

• 🤖 Agent-native stablecoin payments on Cosmos. Same fetchWithPayment(url) mental model as EVM x402 — just a different signature scheme underneath.

• 💰 iUSD’s yield rebates to the ecosystem. Every iUSD your agent holds is productive capital — the issuer doesn’t pocket the T-Bill yield.

• 🌉 Cross-VM out of the box. One client wires an EVM signer (viem) + a Cosmos signer (@cosmjs/*) and lets Skip:Go orchestrate the legs.

• 🔌 One tool, four actions. quote for pricing UX · balance for treasury reads · execute for explicit bridging · pay_url for the full 402 dance.

---

📚 Repos & links

• 🛠️ Skill: payment-skill — install into any AI host with one command

• 📦 SDK: n-payment (v0.23+ for iusd_bridge)

• 🟦 Initia docs: docs.initia.xyz · networks: resources

• 🪙 iUSD on DefiLlama: defillama.com/stablecoin/initia-iusd

• 🏦 Agora AUSD: agora.finance · Wormhole + AUSD partnership

• 🔗 LayerZero OFT: layerzero.network · OFT docs

• 🌉 Wormhole NTT: wormhole.com/products/ntt · deep dive

• 🚀 Skip:Go API: docs.skip.build · /v2/fungible/route

• 🌐 x402 spec: docs.x402.org · Coinbase intro · GitHub

• 🧱 Cosmos SDK MsgSend: bank module reference · @cosmjs/stargate (npm)

• 💧 Faucets: Initia faucet.testnet.initia.xyz · USDC faucet.circle.com · Base Sepolia ETH alchemy.com/faucets/base-sepolia

• 🔍 Explorers: scan.testnet.initia.xyz · scan.initia.xyz