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

# Lago

> Report attributed cloud spend to a Lago billable metric

CostGraph reports each customer's attributed cloud spend to a
[Lago](https://getlago.com) billable metric as usage events. A charge on the
metric turns them into invoices. The shared model, tag rules, and nightly
behavior are on the [Billing exports](/costgraph/integrations/exports/overview)
page.

## Before you begin

* Create a billable metric that aggregates `value` with a **sum**. CostGraph
  offers only metrics it can see in the connected account.
* Attach a charge to the metric. Price per cent, or divide by 100 in the
  metric.
* Copy an API key from **Developers > API keys**.

## Connect

<Steps>
  <Step title="Connect the account">
    In **Integrations**, click **Lago** and enter the API key. If you
    self-host Lago or use a region other than the default, set **API URL** to
    your instance, for example `https://lago.internal`. Leave it empty for Lago
    Cloud. CostGraph verifies the key against Lago before it saves anything,
    and stores it encrypted.
  </Step>

  <Step title="Bind a billable metric">
    Bind a `lago_` tag key to one of your billable metrics.
  </Step>
</Steps>

## Tag spend by customer

The tag value must be a Lago external subscription id, not a customer id. Lago
attributes usage to a subscription, so a customer with two subscriptions needs
the tag to name the one that carries the cloud spend. Lago rejects an event
for a subscription that doesn't exist, and CostGraph records the day with the
rejection instead of billing it.

## Event payload

Each customer-day is one event on the metric. Its `transaction_id` is derived
from the day and the totals, so a retried run counts once. The properties
carry `value`, the amount in cents, and the shared reconciliation fields.

Corrections are sent as the difference and can be negative. The metric must
sum `value` for the total to settle.

## Lago behavior

Lago assigns an event to the period its timestamp falls in. A correction that
arrives while that period's invoice is a draft is included in it. After the
invoice is finalized, Lago doesn't move the event to a later one. Settle the
difference with a manual adjustment in Lago.