**Important:** This feature is available to allowlisted accounts only. Contact your Google representative if you need access to the feature.

<br />

Requests to the [`ReachPlanService`](https://developers.google.com/google-ads/api/reference/rpc/v26/ReachPlanService) must supply OAuth
credentials and a customer ID that your OAuth credentials can access. In
addition, the Google Cloud project associated with your OAuth credentials must
be approved for using this service.

This guide covers authentication details specific to
[`ReachPlanService`](https://developers.google.com/google-ads/api/reference/rpc/v26/ReachPlanService). If you haven't already, first complete
the steps outlined in [Get started](https://developers.google.com/google-ads/api/docs/get-started/introduction), then return to this guide.

## OAuth credentials

In addition to the guidance presented in [Get started](https://developers.google.com/google-ads/api/docs/get-started/introduction), keep the
following points in mind:

1. Your Google Cloud project number must be added to the appropriate allowlist to connect to the [`ReachPlanService`](https://developers.google.com/google-ads/api/reference/rpc/v26/ReachPlanService), even if it's already approved for use with other Google Ads API services. For more information, see the [eligibility requirements](https://developers.google.com/google-ads/api/docs/reach-forecasting#eligibility).
2. You must accept the Google Ads API Terms of Service to connect to the Google Ads API.
3. The user who owns your OAuth refresh token determines which customer IDs you can query in the [`ReachPlanService`](https://developers.google.com/google-ads/api/reference/rpc/v26/ReachPlanService). This informs your integration and is explained in more detail in the following sections.

## Customer IDs

Most services within the Google Ads API operate on specific Google Ads accounts and
campaigns. As a result, most requests require both a customer ID to identify the
target account and [OAuth credentials](https://developers.google.com/google-ads/api/docs/oauth/overview) authorized to access
that customer ID.

However, [`ReachPlanService`](https://developers.google.com/google-ads/api/reference/rpc/v26/ReachPlanService) is meant for video planning
activities that might occur before you establish a specific customer account for
running a campaign.

### Internal tools

If you build tools for internal use within your organization, consider the
following options:

- **Planners without direct client account access:** If your planners don't have access to your clients' Google Ads accounts, generate OAuth credentials using the [single-user authentication flow](https://developers.google.com/google-ads/api/docs/oauth/single-user-authentication) for a user with access to your manager account. Then, create or obtain a Google Ads account for each team using your tool and [link them to your manager
  account](https://support.google.com/google-ads/answer/7459601). When making requests to [`ReachPlanService`](https://developers.google.com/google-ads/api/reference/rpc/v26/ReachPlanService), provide the customer ID corresponding to the user's team.
- **Planners with client account access:** If your planners have access to a Google Ads manager account that manages your clients' accounts, implement the [multi-user authentication flow](https://developers.google.com/google-ads/api/docs/oauth/multi-user-authentication) to allow your application to use your planners' OAuth credentials. You can then pass the customer ID corresponding to the customer plan.

### External tools

If you build tools for third-party or external users, we recommend the following
options:

- **Per-client accounts:** Generate OAuth credentials using the [single-user
  authentication flow](https://developers.google.com/google-ads/api/docs/oauth/single-user-authentication) for a user with access to your manager account. Create a Google Ads account per external client and [link them to your manager account](https://support.google.com/google-ads/answer/7459601). Configure your tool to provide the client's corresponding customer ID when generating plans.
- **User-granted access:** Allow your users to grant your tool access to their accounts using the [multi-user authentication
  flow](https://developers.google.com/google-ads/api/docs/oauth/multi-user-authentication). Once a user grants permission, use the [`CustomerService`](https://developers.google.com/google-ads/api/docs/account-management/listing-accounts) to retrieve the list of Google Ads accounts they can access.

> [!NOTE]
> **Note:** When accessing child accounts through a manager account, remember to set the `login-customer-id` HTTP header to your manager account's customer ID.

Before integrating the API, select one of the preceding approaches based on your
system requirements and identify a few test customer IDs. If in doubt, start
with the **single-user authentication flow** with linked accounts.

## What's next

Learn how to [specify a media plan](https://developers.google.com/google-ads/api/docs/reach-forecasting/media-plan).