---
skill_id: gf-pc-invoice-rail-spec-kit
evaluation: free
quality: agent-decision-grade
functional: true
price_usd_full: 5.49
price_label: $5.49 / unlock
kind: good
category: Finance
challenge: https://lvlltd.com/api/pay?skill=gf-pc-invoice-rail-spec-kit
outline: https://lvlltd.com/skills/gf-pc-invoice-rail-spec-kit/outline.json
runtime_after_unlock: src/index.js createSkill
standards: x402, ERC-7857
completion_pass: functional-v1
---

# Free sample — Invoice Rail Spec Kit

**Skill ID:** `gf-pc-invoice-rail-spec-kit`  
**Unlock:** $5.49 / unlock USDC on Base via x402  
**What you get after pay:** runnable sealed pack (`createSkill().run`) + workbook + templates  

## Summary

End-to-end field maps and state machines connecting classic invoices to agent-presentable USDC payment rails and receipt hooks.

Spec kit that links invoice headers, line items, due windows, and payment references to agent rail packets—amount, asset, chain, memo, invoice_id—plus stale-version and underpay exception paths for reconciliation teams.

## When to use

- Finance still issues PDF or ERP invoices while agents collect Base USDC settlement
- You need one canonical mapping from invoice_id to x402 or wallet settle payload
- Recon fails when invoice revisions outpace what the agent presented at pay time

## Decision-grade outline (free)

1. Map invoice header, line, tax-placeholder, and due fields into a rail packet schema agents can serialize without free-text guesswork
2. Define invoice version pins so agents always cite the revision_id that matches the sealed settle amount
3. Specify post-pay receipt hooks: settle_ref, paid_at, amount, and invoice_id for ERP or ledger import
4. Encode underpay, overpay, and stale-revision exception branches with owner and hold-state labels
5. Produce a buyer settlement summary card that cites invoice_id and rail facts while omitting unnecessary counterparty private fields

## Capabilities

- Invoice-to-rail packet field map
- Revision pin and stale-invoice guards
- Post-pay receipt hook definitions
- Underpay/overpay exception branches
- Buyer settlement summary card template

## Artifacts after unlock

- `invoice-rail-field-map.json`
- `invoice-version-pin-rules.md`
- `post-pay-receipt-hooks.json`
- `buyer-settlement-summary-card.md`

## Detailed description

Invoice Rail Spec Kit is for operators who keep traditional invoices—ERP exports, PDFs, or B2B AR docs—yet settle digital and agent-mediated sales in Base USDC, including x402 unlock paths. The kit maps invoice headers, lines, due windows, and identifiers into a compact rail packet agents can present: amount, asset, chain, memo, and invoice_id with an explicit revision pin so buyers never pay against a superseded total. Post-pay receipt hooks define the fields ops should write back into the ledger or ERP without scraping wallets by hand. Exception branches cover underpay, overpay, and stale revision so support holds and finance re-opens use the same labels. Buyer summary cards restate settlement against invoice_id while minimizing private counterparty data, supporting cleaner support exports. Free outline eval is offered so you can validate the map against your invoice source system before unlock. Purchase settles via x402 Base USDC. This is operational specification craft, not accounting software, tax preparation, legal counsel, or investment advice, and it includes no revenue or collection-rate guarantees. Have finance and compliance owners adapt tax placeholders and jurisdiction rules before go-live.

## Functional runtime (paid)

After verified payment the sealed pack includes:

| Path | Role |
|------|------|
| `src/index.js` | `createSkill`, `run`, `plan`, `checklist` |
| `src/runbook.js` | Outline-driven steps with done_when |
| `src/tools.js` | Tool schemas for agent registries |
| `WORKBOOK.md` | Human/operator procedure |
| `templates/` | Checklist + artifact shells |
| `schemas/output.schema.json` | Result contract |

### Agent snippet (after unlock)

```js
import { createSkill } from "./src/index.js";
const skill = createSkill({ tenantId: "ops", agentId: "buyer" });
const result = await skill.run({
  goal: "Execute Invoice Rail Spec Kit for my catalog",
  context: { skill_id: "gf-pc-invoice-rail-spec-kit" },
  dry_run: false,
});
// result.ok, result.steps, result.artifacts
```

## Pay path

1. Free: this sample + outline.json  
2. `GET https://lvlltd.com/api/pay?skill=gf-pc-invoice-rail-spec-kit` → HTTP 402  
3. Transfer `maxAmountRequired` USDC to `payTo` on Base  
4. `POST /api/pay` with `X-PAYMENT: {"txHash":"0x…","skill":"gf-pc-invoice-rail-spec-kit"}`  
5. Write `sealed_pack.files` to disk or use install-unlocked-pack.mjs  
6. Re-redeem anytime with the same verified txHash  

## Honesty

- No revenue, conversion, or uptime guarantees  
- Not legal, tax, medical, or investment advice  
- Crypto transfers are irreversible  
- Confirmed unlocks only for proof strips (/api/proof)  

*Public `/sealed/gf-pc-invoice-rail-spec-kit/` is teaser-only. Full `src/` is paywalled under locked sealed delivery.*