> ## Documentation Index
> Fetch the complete documentation index at: https://lago-ftr-wallet-improvements.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Overview

> Lago automatically generates invoices for each customer according to the plan model.

When a new invoice is generated, Lago also sends an `invoice.created` webhook
([learn more](/api-reference/webhooks/messages)).

When an invoice is linked to an add-on, another type of webhook is sent, called
`invoice.add_on_added`.

## Invoice object[](#invoice-object "Direct link to heading")

Invoices include (but are not limited to):

* Invoice number;
* Billing period;
* Customer information;
* Fees; and
* Taxes.

You can [download invoices](/guide/invoicing/download-invoices) or use the
[invoice object](/api-reference/invoices/invoice-object) to create your own invoice
template.

<Tip>
  You can also use the invoice object to transmit information to your accounting
  software or payment service provider.
</Tip>

## Invoice numbering[](#invoice-numbering "Direct link to heading")

With Lago, invoice numbering is generated every time an invoice is finalized. You have the flexibility to customize how invoice numbers are incremented to align with your organizational structure and customer management approach.

* **Invoice numbering per customer**: This setting is designed to increment invoice numbers individually for each customer.
  It ensures that each customer has their own unique sequence of invoice numbers, separate from other customers.
  This approach is ideal for maintaining distinct and isolated numbering patterns for each customer, aiding in clear tracking and accounting processes.
* **Invoice numbering across the organization**: Opting for this method applies a global sequence for incrementing invoice numbers across your entire organization. Instead of having individual sequences for each customer, all invoices within the organization follow a single, unified numbering system. This creates a continuous and organization-wide sequence for all invoice numbers, simplifying the invoice management process. In that case, invoices are incremented per month (dynamic value used is `YYYYMM`).

## Invoice prefix customization[](#invoice-prefix-customization "Direct link to heading")

Lago also allows you to customize the prefix for documents, including invoices and credit notes.
By default, Lago auto-generates this prefix by combining the first three letters of your organization's name with the last four digits of your organization ID. However, you have the flexibility to fully customize this field to better align with your organization's branding or numbering conventions. This feature ensures clarity and consistency across your documents while allowing you to maintain a professional and personalized appearance in your invoicing system.

## Custom invoice grouping[](#invoice-grouping "Direct link to heading")

Grouping invoice line items in a way that provides clearer insight for your customers can be more beneficial than sticking to the default charge setup in Lago.

For instance, as an AI service provider, you might prefer to regroup all fees associated to one charge by a specific `model` used by a customer, without the need to individually list each model in Lago.

When setting up a charge with a `standard` charge model, you can use `model_name` as an event property in the `grouped_by` attribute. If every event reported to Lago includes a `model_name`, Lago is capable of adjusting your invoice so that charges are organized under the respective model name for that particular charge. Consequently, Lago will also automatically allocate the usage costs for each model.

You can specify multiple `grouped_by` keys for your charge; the order you set them in dictates how they will be displayed on the invoice, affecting the presentation of charges.

<Note>
  The `grouped_by` feature is exclusively available for the `standard` charge model.
</Note>