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

# Customer.io - How do I link my account?

# Overview

To authenticate with Customer.io, you will need:

1. **Subdomain** – Enter `cdp` for the US region or `cdp-eu` for the EU region.
2. **API Key** – A key generated from the Customer.io integration settings.

This guide walks you through creating a Customer.io API key.

### Prerequisites

* You must have a Customer.io account with access to **Data & Integrations**.

### Instructions

#### Step 1: Getting authentication credentials

1. In Customer.io, go to **Data & Integrations** > **Integrations** and click **Add Integration**.

<img src="https://mintcdn.com/nango/8izclGoLSed7AceQ/api-integrations/customer-io/create_integrations.png?fit=max&auto=format&n=8izclGoLSed7AceQ&q=85&s=b4cd89c43fb7319645483680354994bd" width="1921" height="790" data-path="api-integrations/customer-io/create_integrations.png" />

2. Find and select the **Customer.io API** integration.
3. Give the integration a name.
4. Optionally, send a test call using the provided API key before saving.

<img src="https://mintcdn.com/nango/8izclGoLSed7AceQ/api-integrations/customer-io/send_request.png?fit=max&auto=format&n=8izclGoLSed7AceQ&q=85&s=ce0310f2945fe0966443fdfcfcc0bcd7" width="1921" height="750" data-path="api-integrations/customer-io/send_request.png" />

5. Click **Complete Setup** to save your credentials. Copy the API key shown — you will need it when connecting your account via Nango.

<img src="https://mintcdn.com/nango/8izclGoLSed7AceQ/api-integrations/customer-io/api_key.png?fit=max&auto=format&n=8izclGoLSed7AceQ&q=85&s=99acb63b53a9858490ae87eb0fae622b" width="2504" height="1218" data-path="api-integrations/customer-io/api_key.png" />

#### Step 2: Choose your subdomain

* Enter `cdp` for the **US** endpoint (`https://cdp.customer.io`).
* Enter `cdp-eu` for the **EU** endpoint (`https://cdp-eu.customer.io`).

#### Step 3: Enter credentials in the Connect UI

Once you have your **API key** and know your **subdomain**:

1. Open the form where you need to authenticate with Customer.io.
2. Enter your **Subdomain** and **API key** in their respective fields.
3. Submit the form, and you should be successfully authenticated.

<img src="https://mintcdn.com/nango/8izclGoLSed7AceQ/api-integrations/customer-io/form.png?fit=max&auto=format&n=8izclGoLSed7AceQ&q=85&s=4465f92cb6400ba3165f2309f4f99997" style={{maxWidth: "450px" }} width="500" height="701" data-path="api-integrations/customer-io/form.png" />

You are now connected to Customer.io.