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

# Fee Configuration

> Sponsor account setup, fee ceilings, and the trade-offs behind each knob.

The facilitator pays Stellar network fees on behalf of buyers and sellers. This page covers the knobs that control how much it can spend per transaction and in aggregate.

## The sponsor account

* One Stellar account per facilitator instance.
* Holds XLM only. No other assets.
* Its secret key lives in `SPONSOR_SECRET_KEY`.

Do not use a personal or hot-wallet key. Create fresh at deployment.

## Per-transaction ceiling

`SPONSOR_FEE_CEILING_XLM` caps the Stellar fee the facilitator will pay for one settlement. Two forces pull in opposite directions:

* **Higher ceiling** = more resilience to fee spikes, less user-visible failure.
* **Lower ceiling** = predictable burn rate, less loss on runaway RPC estimates.

Default is `0.1 XLM`. Reasonable production values sit between `0.05` and `0.5`. Above that you are almost always paying for an RPC misestimate.

When a settlement's estimated fee exceeds the ceiling, `/settle` returns `fee_ceiling_exceeded`. This is one of the recoverable errors and worth surfacing to the seller.

## Balance alerts

* `SPONSOR_MIN_BALANCE_XLM` is the low-water threshold.
* `SPONSOR_ALERT_WEBHOOK` receives a POST when balance dips below the threshold.

Size the threshold to at least 24 hours of expected burn. Alert routing should page a human, not fill an inbox.

## Estimating burn rate

The `x402_sponsor_fees_paid_xlm_total` counter is monotonic. Over a stable interval:

```text theme={null}
burn_rate_xlm_per_day = (fees_paid_at(t+24h) - fees_paid_at(t)) / 1 day
```

Use the observed rate for reordering and top-ups, not the estimated one.

## Charging users

Today, the operator absorbs sponsor cost. If you want to pass fees through, run your own facilitator and factor the cost into your sellers' quoted prices (e.g. add a percentage to `amount` in your middleware before responding with `PaymentRequirements`). The wire protocol has no built-in fee-pass-through.

## Related

* [Configuration Reference](/guides/operators/configuration-reference)
* [Observability](/guides/operators/observability)