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

# Connect the Fees Engine to Midaz

> How the Fees Engine connects to Midaz — what it reads from the ledger, and the deploy-time configuration that wires them together.

The **Fees Engine** is part of Midaz, deployed as an independent service, and it works by **calculation**: your application asks it to compute the fees for a transaction, and it returns the result. Your application then submits the transaction — fees included — to Midaz. The Fees Engine **reads** from Midaz to do its job, but it never writes to the ledger; recording the transaction is your application's step.

For where this sits in the bigger picture, see [Building a complete core banking](/en/building-a-complete-core-banking).

## What the Fees Engine uses Midaz for

***

The Fees Engine **reads** from Midaz for two things — it doesn't post anything back:

* **Resolving accounts** — it looks up the accounts involved, by alias, through Midaz's **Onboarding API**, so a fee targets real accounts.
* **Volume-based billing** — it counts transactions per route through Midaz's **Transaction API**, which feeds period and volume billing.

The fee itself is **calculated and returned to the caller**. Your application records it in the ledger when it submits the transaction — the Fees Engine doesn't write to Midaz.

## Connection configuration

***

The connection is set with environment variables when the Fees Engine is deployed (in its ConfigMap) — not by your application. Your app only calls the Fees Engine's own API.

| Variable                | Default / Required        | Description                                                                                                                                          |
| ----------------------- | ------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------- |
| `MIDAZ_ONBOARDING_URL`  | **Required**              | Base URL of Midaz's Onboarding API, used to resolve accounts by alias. In local setups: `http://midaz-ledger:3002/v1/`.                              |
| `MIDAZ_TRANSACTION_URL` | **Required**              | Base URL of Midaz's Transaction API, used to count transactions per route for volume-based billing. In local setups: `http://midaz-ledger:3002/v1/`. |
| `CLIENT_ID`             | Used for auth             | Client ID the plugin uses to authenticate to Midaz (machine-to-machine).                                                                             |
| `CLIENT_SECRET`         | Used for auth             | Client secret paired with `CLIENT_ID`.                                                                                                               |
| `PLUGIN_AUTH_ENABLED`   | `false`                   | Enable authentication through Access Manager. Set to `true` in production.                                                                           |
| `PLUGIN_AUTH_ADDRESS`   | `http://plugin-auth:4000` | URL of the Access Manager (`plugin-auth`) service that issues the tokens.                                                                            |

<Note>
  Both `MIDAZ_ONBOARDING_URL` and `MIDAZ_TRANSACTION_URL` are required — the plugin won't start without them. In local setups both point at the same Midaz host (`midaz-ledger:3002`); in production they point at your deployed Midaz APIs.
</Note>

## Authentication

***

The Fees Engine authenticates to Midaz through **Access Manager**. It exchanges its `CLIENT_ID` / `CLIENT_SECRET` for an application token and calls Midaz with that token — the same machine-to-machine pattern used across the platform.

In **multi-tenant** deployments, the per-tenant credentials come from **AWS Secrets Manager** rather than the static `CLIENT_ID` / `CLIENT_SECRET`; Access Manager then issues the token from those credentials, so each tenant's calls reach the right ledger. Multi-tenant mode requires authentication to be enabled.

→ [Access Manager](/en/platform/access-manager/access-manager)

## See it in Lerian

***

* The full integration journey across the pieces: [Building a complete core banking](/en/building-a-complete-core-banking)
* What the Fees Engine does: [What is Fees Engine?](/en/midaz/fees/fees-engine-overview)
* Deploy the stack: [Helm charts](/en/platform/helm/helm-overview)