First, you will need an access to the Google Ad Manager network. If the account was not created, you should create it first. To do that, follow the steps below.

1. Open Google API Console.
2. Create a new project.

3. After the project has been created, you need to go into it and click Create credentials.

4. Select a Service account in the dropdown.

5. In the form for creating a service account, enter the Account name and click Done. The account ID will be assigned automatically, you can skip the optional steps.

6. Go to the service account.

7. Go to tab Keys. Press the Add key button and select Create new key.

8. Select JSON key type and press Create.

9. The key will be created and saved on the user’s device in the folder for downloaded files. The key file can be opened with a code editor (e.g. Notepad++).