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

# LagoDestinationOptions

[**@ai-billing/lago**](../index)

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[@ai-billing/lago](/docs/sdk/ai-billing/reference/lago/typedoc/index) / LagoDestinationOptions

# Interface: LagoDestinationOptions\<TTags>

Defined in: [lago-destination.ts:24](https://github.com/narevai/ai-billing/blob/main/packages/lago/src/destination/lago-destination.ts#L24)

Options for [createLagoDestination](/docs/sdk/ai-billing/reference/lago/typedoc/functions/createLagoDestination).

Lago ingests metered usage as events tied to an `external_customer_id` plus a `code` (billable metric
code). This destination extracts identity from billing event tags, builds default `properties` from the
event (usage + tags), and always sets `cost_nanos` and `currency` from BillingEvent.cost. Callers
must supply a defined `cost` on each event; the implementation asserts it is present and may throw at
runtime if it is omitted.

## Type Parameters

### TTags

`TTags` *extends* `DefaultTags` = `DefaultTags`

The shape of the tags object, extending DefaultTags.

## Properties

### apiKey

> **apiKey**: `string`

Defined in: [lago-destination.ts:28](https://github.com/narevai/ai-billing/blob/main/packages/lago/src/destination/lago-destination.ts#L28)

Lago API key used for `Authorization: Bearer ...`.

***

### apiUrl?

> `optional` **apiUrl?**: `string`

Defined in: [lago-destination.ts:30](https://github.com/narevai/ai-billing/blob/main/packages/lago/src/destination/lago-destination.ts#L30)

Base URL for the Lago API. Defaults to `https://api.getlago.com`.

***

### meterCode?

> `optional` **meterCode?**: `string` | ((`event`) => `string`)

Defined in: [lago-destination.ts:36](https://github.com/narevai/ai-billing/blob/main/packages/lago/src/destination/lago-destination.ts#L36)

Lago billable metric code (`event.code`), or a function that derives the code from the billing event.

Defaults to `'llm_usage'`.

***

### externalCustomerIdKey?

> `optional` **externalCustomerIdKey?**: keyof `TTags`

Defined in: [lago-destination.ts:42](https://github.com/narevai/ai-billing/blob/main/packages/lago/src/destination/lago-destination.ts#L42)

Tag key used to read the Lago `external_customer_id`. When omitted, common tag keys are checked:
`userId`, `externalCustomerId`.

***

### mapMetadata?

> `optional` **mapMetadata?**: (`event`) => `Record`\<`string`, `string` | `number` | `boolean`>

Defined in: [lago-destination.ts:54](https://github.com/narevai/ai-billing/blob/main/packages/lago/src/destination/lago-destination.ts#L54)

Optional override for the `properties` payload sent to Lago.

When omitted, metadata is built from buildMeterMetadata and includes:

* token/usage dimensions
* `tag_*` values from event tags

Note: this destination always merges `cost_nanos` and `currency` into `properties` from `event.cost` via
non-null assertion. Missing BillingEvent.cost is not supported and will throw when converting.

#### Parameters

##### event

`BillingEvent`\<`TTags`>

#### Returns

`Record`\<`string`, `string` | `number` | `boolean`>