Test Account

Google Ads client account would be an account you're making API calls against. You need necessary permissions to operate on this account, such as fetching reports or making changes to campaigns.
For testing purposes, you may want to create a test client account. However since test accounts don't serve ads, some features would be missing there - make sure to review this page to figure out what type of account would work best for your specific scenario and how to create one.

API Access

To be able to use the Google Ads API you'll need a few things:

• a Google Ads manager account. If you don't have it already, here's how to create one

• Developer token which lets your app connect to the Google Ads API and should be added to requests headers on every call. Here's an official guide on how to apply for a developer token.
  Please note that to make API calls against your production account, you need to request Basic Access or Standard Access for your developer token during the token application process. That very first developer token can only be used to make calls to your test client accounts

• Google API Console project. The project is used for generating an OAuth 2.0 client ID and secret for your app. The ID and secret can then be used to generate the OAuth 2.0 credentials needed in API calls to the Google Ads account. The project also enables the API to accept calls. Follow the steps outlined here to create a new project and generete OAuth credentials.
  Note:
  -- make sure to save the Client ID and Secret somewhere safe - you'll need them later when configuring the integration within the integration.app console
  -- add https://api.integration.app/oauth-callback Redirect URI

Publish your app

If you want your OAuth app to be accessible to other users outside of your organization, you may want to submit it for review. You can find more information about the process here