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

# Real-Time Account Updater API Headers

All calls to Real-Time Account Updater must include the following API headers:

| Header        | Format | Example                                | Description                                |
| :------------ | :----- | :------------------------------------- | :----------------------------------------- |
| Authorization | String | Bearer \<api key>                      | The API key you created during onboarding  |
| X-Merchant-ID | String | "9bb8592c-cb99-48f7-907e-f97de930fc5c" | Identifies the merchant making the request |

The first header is used for [authentication](#authentication), and the **X-Merchant-ID** clarifies which merchant sent the request. This merchant identification is especially important for platform providers; [learn more below](#merchant-identification) .

## Authentication

The Pagos platform uses API keys to authenticate requests to all our services. See our [API Authentication](/authentication/authentication-overview) guide for full instructions on generating API keys and authenticating with the Pagos APIs.

## Merchant Identification

To better support Pagos users with merchant-to-platform hierarchies, Real-Time Account Updater includes an `X-Merchant-ID` attribute in the header that sits underneath the API User. The relationship between API User and merchant is **1..n**; an API User can have **n** merchants but a merchant will be associated with only **one** API User. Pagos uses this merchant ID to pull the applicable network-specific MIDs to send to the networks for account updates.

We'll assign this unique merchant ID to you at the time of onboarding. If your business doesn't operate as a platform, you'll always use the same ID in the header of each call.