Go to, https://admin.google.com > Admin Roles
Click Create new Role.
Define Role name and description.
Choose API permission scopes,
Groups > Read
Users > Read
Verify chosen roles and Click create role.
Click Assign Role > Choose google service user.
Confirm roles assigned and privileges.
Go to API explorer, and Test assigned roles and privileges.
https://developers.google.com/admin-sdk/directory/v1/reference/groups/get
Enter your Google group mail address > Execute.
Make sure execution status 200.
Click Allow.