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

# Introduction

> What the QX API does and how to start.

The QX API gives the system of an organization access to the data of that organization. With the API, your system:

* creates and reads the contacts;
* creates and reads the collections;
* sends the documents, reads the fields that the reading extracts and writes the field answers;
* lists the packs and the requirements of each pack.

## Address

All calls use this base address:

```text theme={null}
https://app.useqx.com/api/v1
```

The API returns JSON. It receives JSON, and a file upload uses `multipart/form-data`.

## First steps

1. Ask QX for an API key for the organization. See [Authentication](/en/authentication).
2. Call `GET /packs` with the key in the `Authorization` header.
3. Read the packs in the `data` field of the response.

```bash theme={null}
curl https://app.useqx.com/api/v1/packs \
  -H "Authorization: Bearer qx_sua_chave"
```

Then follow the [Quickstart](/en/quickstart). It creates a contact and a collection, sends an invoice and reads the fields of the invoice.

## Rules for every call

* Call the API from the server of your system. The API does not send CORS headers, so the browser blocks the response.
* The API returns each error in the RFC 9457 format. See [Errors](/en/errors).
* A list returns one page at a time. See [Pagination](/en/pagination).
* The field names, the enum values and the error codes are in English. The explanation of each error follows the language of the organization, Portuguese or English. See [Errors](/en/errors).