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

# Subtotal API

> Make HTTP requests in your preferred programming language.

## Introduction

The Subtotal API is built on REST principles, ensuring a stateless, scalable, and reliable interface for interacting with merchant accounts on behalf of customers.

## API Reference

Our [API reference](/docs/api-reference) provides all the necessary details to integrate Subtotal's features into your application, including endpoint descriptions, request and response formats, and examples.

## Base URL

Append an endpoint to the base URL root address to form a complete request URL.

```
https://api.subtotal.com
```

## Authentication

All requests must include an API key for authentication.

Include the following header in each request:

```json theme={null}
headers = {
  "X-Api-Key": "{yourkeyvalue}"
}
```

## Authorization

We reserve the *Authorization* header for endpoints that require a [connection token](/docs/api-reference/connections/create-connection-token).

```json theme={null}
headers = {
  "Authorization": "Bearer: {connection_token}"
}
```