AI-agent-ready crypto billing.For indie hackers and AI-first startups.

You are integrating TxNod, a non-custodial crypto payment gateway, into this project. Your job is to study the docs, wire the integration surface that fits this project, and produce an integration PLAN — do not write integration code yet.

## 1. Read the docs first

Start at https://docs.txnod.com/llms.txt — every linked page has a sibling .md raw form, and https://docs.txnod.com/llms-full.txt is the same corpus bundled in one file. Always check the npm registry for the current SDK version (`npm view @txnod/sdk version`); never rely on a memorized version number.

## 2. Pick the integration surface for THIS project

- **TypeScript / JavaScript / Node.js project:** install the typed SDK with `npm install @txnod/sdk@latest`. The SDK ships its own version-matched docs locally — read these before the website once installed:
  - node_modules/@txnod/sdk/AGENTS.md — entry point with read-order and non-negotiable invariants
  - node_modules/@txnod/sdk/docs/ — full markdown reference, frozen at the installed version

  The SDK's dist/index.d.ts is the source-of-truth for types — when markdown and .d.ts disagree, trust the .d.ts.
- **Any other language (Python / Go / Ruby / PHP / Rust / Java / .NET / etc.):** there is no language SDK. Use the REST API directly. Read https://docs.txnod.com/api for the OpenAPI surface, sign every outbound request with HMAC, and verify every inbound webhook yourself with a constant-time HMAC compare plus a ±300s timestamp tolerance — BEFORE parsing the body.

## 3. Sandbox-first integration path

**Default to sandbox.** If the human owner has a sandbox project (any operator can create one in 30 seconds at https://txnod.com/projects/new-sandbox), they hand you four credentials: TXNOD_PROJECT_ID, TXNOD_API_SECRET (sk_sandbox_*), TXNOD_WEBHOOK_SECRET, plus a sandbox PAT. Sandbox projects auto-provision testnet xpubs — no wallet wizard, no hardware device, no faucet. You drive the entire integration loop with sandbox-simulate calls and the webhook handler observes real signed events with mode: 'sandbox'. **If they have a sandbox project, paste those credentials and proceed; otherwise read § 4 below for the mainnet flow.**

## 4. Human-only prerequisites (mainnet only)

The following must be done by the human owner of this project — an agent cannot perform them:
- Sign in at https://txnod.com (invite-only — request access at https://txnod.com/apply if needed).
- Add a hardware-wallet xpub via the Wallets wizard. **Connect Ledger over WebHID or Trezor over WebUSB is the recommended onboarding path. Ledger covers every chain TxNod supports (BTC, ETH + ERC-20 stables, Polygon PoS, BNB Smart Chain, TRON + TRC-20 USDT, Cardano, TON). Trezor covers BTC, ETH, Polygon, BSC, and Cardano (Model T or newer required for Cardano — Trezor One is unsupported); for TRON, use Ledger; for TON, use Ledger or TON Connect.** The dashboard reads the account-level extended key from the device and rewraps it to the exact format TxNod's per-chain validator expects — no copy-paste, no manual conversion. Do not copy values out of Ledger Live or Trezor Suite "Advanced logs" panels; the wizard will reject them.
- Create a project, enable the coins to accept, set a webhook URL.
- Generate an API secret pair and copy the webhook signing secret (shown exactly once).

You will need these values before writing code: TXNOD_PROJECT_ID, TXNOD_API_SECRET, TXNOD_WEBHOOK_SECRET, plus the webhook URL the human registered (your route must match).

## 5. Produce a plan, do not implement yet

Output a written plan covering:
- Files to create or modify, with one-line role descriptions
- Env vars the project reads, and where (server-side only)
- Webhook route shape: path, runtime, signature verification, idempotency strategy
- Open questions and any missing values, listed by name

Wait for explicit user approval and the missing values before writing code. If a required value is unknown, ask — do not invent placeholders, do not stub.

## 6. Constraints (non-negotiable)

- Non-custodial: never store, log, or transmit a private key, mnemonic, or seed. Only public xpubs / stake addresses ever enter the system.
- Verify every inbound webhook with verifyWebhookSignature from @txnod/sdk (TypeScript) or your own constant-time HMAC + ±300s timestamp check (any other language) BEFORE parsing the body.
- Treat event_id as the idempotency key when crediting users — webhooks may be retried.
- API secret is server-side only; never bundle it into client code.
- Default to sandbox mode (no on-chain interaction); fall back to testnet only when the integrator explicitly asks; mainnet only after explicit human approval.

## 7. Stop when the plan is implemented

After the plan is approved AND missing values are supplied, implement only what's in the approved plan, run the project's existing tests, and stop. Do not deploy, do not push, do not modify wallet/binding config in the dashboard — those changes belong to the human.