Return to the Google Admin Console > Security > Settings
Choose App Access Control
Choose Manage Domain-Wide Delegation
In this screen, Click Add New
copy the Client ID value that you copied from the Service Account and paste it into the Client ID field.
Then copy and paste the following comma-separated list of API scopes into the OAuth Scopes section and click Authorize.
Keep these credentials
Click View Client ID on your Service Account and keep this tab open as you will need the Client ID and Service account email address later in this setup.
Classroom Teachers Group
In your Google Admin Console go to Groups, then click the group named Classroom Teachers (email@example.com). Click Manage Users in Classroom Teachers, then add your teachers to this group to enable the Google Classroom feature for your teachers.
Note: Teacher accounts can not be members of a sub-group under the Google Classroom Teachers group. The Teacher accounts must be added directly into the 'classroom_teachers' group