> ## Documentation Index
> Fetch the complete documentation index at: https://billing-help.nace.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Billing overview

> What NAPA is and why we use it

## What is NAPA?

**NAPA** is NACE’s billing automation. It takes **contracts** and **timesheets** (and expenses when needed) and creates **invoices** that are correct and fully traceable.

## Why we use NAPA

In service industries (e.g. healthcare locums, legal, oil & gas), small billing mistakes can add up to **3–5% revenue leakage**. NAPA:

* Builds invoices from the actual contract and approved time/expenses
* Applies billing rules so line items match the contract
* Keeps a clear link from every line item back to the source (so we can show “this rate comes from contract X, section Y”)
* Reduces manual errors and speeds up approval

## What happens end to end

1. **Input** — Contract + timesheet (+ expenses). Data can come from Barton timesheets (synced hourly), Navan (travel expenses), and Salesforce (contracts and rates).
2. **Processing** — NAPA pulls the data together, applies billing rules, and checks that everything aligns with the contract. Some cases are auto-approved; others are sent for your review.
3. **Output** — An invoice draft is created, then (after review if needed) approved and sent out—e.g. to NetSuite, the client portal, and by email.

## The Billing app

The **Billing app** is the screen you use to upload documents, trigger or monitor runs, review and approve invoices, and handle disputes. For how to use it day to day, see [Billing app overview](/frontend/overview) and [Using the Billing app](/frontend/using-the-app).