> ## Documentation Index
> Fetch the complete documentation index at: https://docs.stable.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# Settle invoices

> Settle invoices on Stable using ERC-3009 with deterministic nonces derived from invoice metadata for automatic reconciliation.

Each invoice maps to a unique, deterministic nonce derived from invoice metadata: invoice number, parties, amount, and due date. This nonce drives settlement via [ERC-3009](/en/explanation/erc-3009) and creates an immutable receipt that can be reconciled with existing accounting systems.

## How it works

Both the buyer and the vendor independently compute the same nonce from the same invoice metadata. No external registry is required to coordinate payment.

The nonce is derived deterministically:

```
nonce = keccak256(invoiceNumber, vendor, buyer, amount, dueDate)
```

When the buyer signs the ERC-3009 authorization using this nonce, the on-chain settlement event serves as a tamper-proof payment receipt.

### Settlement flow

1. **Invoice issued**: the vendor creates an invoice with a unique number, amount, and due date.
2. **Nonce computed**: both parties independently derive the same nonce from the invoice metadata.
3. **Buyer signs**: the buyer signs an ERC-3009 authorization off-chain using the deterministic nonce. The `validBefore` field can be set to the due date plus a grace period.
4. **Settlement**: the buyer or vendor submits `transferWithAuthorization` on-chain. Settlement confirms in under a second.
5. **Reconciliation**: the emitted `AuthorizationUsed` event contains the nonce, linking the on-chain settlement to the exact invoice. The `Transfer` event in the same transaction verifies sender, recipient, and amount.

### Double-payment prevention

The nonce is consumed on-chain upon payment. The same invoice cannot be settled twice; resubmitting an authorization with an already-used nonce reverts.

## What makes it different

Traditional B2B invoicing involves bank wires (1–5 business days), manual reconciliation, and no cryptographic proof of payment tied to the invoice itself. With deterministic nonces, the on-chain payment is self-documenting: the nonce links the settlement to the exact invoice, and the blockchain event log provides an immutable audit trail.

| **Aspect**     | **Traditional (bank wire)**             | **Stable (ERC-3009)**                                     |
| :------------- | :-------------------------------------- | :-------------------------------------------------------- |
| Settlement     | 1–5 business days                       | Under 1 second                                            |
| Reconciliation | Manual matching against bank statements | `AuthorizationUsed` event links payment to invoice nonce  |
| Payment proof  | Bank confirmation letter                | On-chain transaction, cryptographically linked to invoice |
| Intermediaries | Correspondent banks                     | None                                                      |
| Fees           | Wire fees (\$15–45) + FX spread         | \~0.00021 USDT0 (or 0 with Gas Waiver)                    |

**See also:**

* [ERC-3009 (Transfer With Authorization)](/en/explanation/erc-3009)
* [Gas Waiver](/en/how-to/integrate-gas-waiver)