> ## 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. # Fee debt > Keep an unpaid fee as a debt that the payer's next credits settle, oldest first, instead of refusing the transaction. By default, Midaz refuses a transaction when the payer cannot fund its fees. A **deferrable** fee changes this. The payer pays the part of the fee that its available amount covers. The rest becomes a **fee debt**, and the transaction goes through. Later credits to the payer settle the debt. Fee debt is off by default. It applies only to fees that you mark as deferrable. ## Make a fee deferrable *** Set `deferrable: true` on a fee when you [create](/en/reference/products/midaz/v2/create-package) or [update](/en/reference/products/midaz/v2/update-package) its fee package. * Only a fee with `isDeductibleFrom: false` can be deferrable. Midaz refuses a deductible fee that is also deferrable with error `0530`. * A deferrable fee opens a debt only in a `/v2` direct transaction. In a `/v2` hold, Midaz refuses an unfunded fee with error `0018`. * When a balance already has 256 open fee debts, Midaz refuses a new unfunded deferrable fee on it with error `0018`. **Example.** A payer holds 105 and sends 100 with a deferrable fee of 10. The transaction moves 105: the payment of 100 and 5 of the fee. The other 5 becomes a fee debt. The transaction metadata key `feeDebtOpenings` records the debt. ## How a debt is settled *** A credit to the payer's balance through the `/v2` API settles its open fee debts, oldest first. This includes direct transactions, commits, and reversals. A credit that is smaller than a debt settles part of it. Each settlement moves the value from the payer's balance to the fee account of the debt. Midaz records these movements as operations of type `FEE_SETTLEMENT`, and the transaction metadata key `feeDebtSettlements` records the settled debts. To settle debts without a credit, use [Collect open fee debts](/en/reference/products/midaz/v2/collect-a-balance-s-open-fee-debts). Send the `accountAlias` of the payer, and optionally a `balanceKey` and a `maxAmount`. * Midaz pays the open debts of that balance from its available amount, oldest first, and charges no fee on the collection. * The response gives the `collected` amount and the `transactionId` of the collection. * When nothing is collected, the response gives `collected: "0"` and Midaz creates no transaction. * You cannot revert a collection. Midaz refuses it with error `0089`. ## Reversals and fee debt *** When you [revert](/en/reference/products/midaz/v2/revert-transaction) the transaction that opened a debt, the payer gets the whole fee back: * The reversal returns the part of the fee that the payer paid in the original transaction. * Midaz cancels the part of the debt that is still open. * Midaz refunds the part that later credits settled. The fee account pays the refund, and Midaz records it as operations of type `FEE_REFUND`. On `/v2`, the refund then settles the payer's other open debts, oldest first. A revert of a credit that settled a debt can reopen that debt for the settled amount. When the fee-debt record of a transaction is not complete yet, Midaz refuses the revert with error `0529` (HTTP 409) and moves nothing. Try again later. ## Read fee debts *** * [List fee debts](/en/reference/products/midaz/v2/list-the-fee-debts-of-a-ledger-oldest-first) gives the debts of a ledger, oldest first. Filter by `account_alias`, `balance_key`, and `status` (`open` or `settled`). With `account_alias`, the response also gives `openTotal`, the total that the balance owes. * [Retrieve a fee debt](/en/reference/products/midaz/v2/get-a-fee-debt) gives one debt with its `remaining` amount and its history of changes. Listing and reading fee debts needs the `midaz/fee-debts` permission with `get`. Collecting fee debt needs `post`. Each change has one of these kinds: | Kind | What happened | | - | - | | `opened` | The payer could not fund the fee, and the debt opened. | | `settled` | A credit or a collection paid part or all of the debt. | | `canceled` | A revert of the original transaction canceled the open part. | | `reopened` | A revert took back a settlement, and that amount is owed again. | | `refunded` | A revert of the original transaction returned a settled part to the payer. | ## Accounts and balances with fee debt *** Midaz refuses to delete a balance, or to delete or close its account, when: * The balance owes fee debt (error `0527`). Credit the balance or collect the debt first. * Other balances owe fee debt to the balance (error `0528`), for example a fee account. Credit the balances that owe the debt first. ## Before you enable fee debt *** * Run Midaz v4.2.0 or later on every ledger instance before you set `deferrable` on a fee. An earlier version cannot complete a transaction that carries fee debt. After you set it, do not roll the ledger back to an earlier version. * The ledger keeps open fee debts in Valkey. Valkey must be persistent and keep these keys. See [Configuring dependencies](/en/platform/deploy/midaz/midaz-dependencies#valkey). This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.