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

# Working with invoices

> addInvoice, addOrderInvoiceFile — issuing an invoice in Base and replacing it with one from your ERP

Base can either issue an invoice itself, or take a ready-made invoice issued externally (typically in your ERP/accounting system) and attach it to an order.

## Issuing an invoice in Base

[`addInvoice`](https://api.baselinker.com/index.php?method=addInvoice) issues an invoice for an order using a chosen numbering series.

| Parameter   | Type | Description                                                                                                                                                                        |
| ----------- | ---- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `order_id`  | int  | Order ID.                                                                                                                                                                          |
| `series_id` | int  | Numbering series ID — list available series with [`getSeries`](https://api.baselinker.com/index.php?method=getSeries).                                                             |
| `vat_rate`  | text | Optional. `"DEFAULT"` (per numbering series), `"ITEM"` (rate from the order line item), `"EXPT"`/`"ZW"` (VAT exempt), `"NP"`, `"OO"` (reverse charge), or a specific number 0–100. |

```json theme={null}
{ "order_id": 4553562, "series_id": 1 }
```

The response returns `invoice_id`, which you then use for downloading the file ([`getInvoiceFile`](https://api.baselinker.com/index.php?method=getInvoiceFile)) or listing invoices ([`getInvoices`](https://api.baselinker.com/index.php?method=getInvoices)).

## Replacing it with an invoice from an external system

If you issue invoices in your own ERP (and don't want to duplicate numbering in both Base and your system), use [`addOrderInvoiceFile`](https://api.baselinker.com/index.php?method=addOrderInvoiceFile) — it replaces the standard Base invoice with your own PDF (or XML, for countries where that's allowed, e.g. Brazil).

| Parameter                 | Type        | Description                                                               |
| ------------------------- | ----------- | ------------------------------------------------------------------------- |
| `invoice_id`              | int         | Base invoice ID (must already exist — e.g. created via `addInvoice`).     |
| `file`                    | text        | PDF (or XML) in base64, with a required `"data:"` prefix.                 |
| `external_invoice_number` | varchar(30) | Invoice number from your system — overwrites the number assigned by Base. |

```json theme={null}
{
  "invoice_id": 153845,
  "file": "data:4AAQSkZJRgABA[...]",
  "external_invoice_number": "FV/2024/001"
}
```

### Recommended flow

1. Your ERP issues an invoice (number, PDF).
2. In Base, create an invoice for the order via `addInvoice` (you just need a valid `series_id` — the specific number/rate doesn't matter much since you'll overwrite it shortly).
3. Call `addOrderInvoiceFile` with the `invoice_id` from step 2, attach the PDF from your ERP, and set `external_invoice_number` to the real number from your system.
4. Forwarding the invoice further to the marketplace (if the integration supports it) is typically tied to a specific order status — configured per integration, similar to [tracking numbers](/en/objednavky/prepravni-stitky#how-the-tracking-number-gets-back-to-the-order-source). Timing (batches, not instant) is described in [Automation and webhooks](/en/objednavky/automatizace-a-webhooky#delivering-tracking-numbers-and-invoices-to-the-marketplace).

<Tip>
  If you have more complex numbering-series logic (different cost centers, countries, VAT regimes), consider driving it via [extra fields](/en/objednavky/extra-pole) rather than hardcoded rules in the integration — it's easier to maintain. Discuss non-trivial scenarios with the implementation team.
</Tip>