Go to, https://admin.google.com > Admin Roles

Click Create new Role.

Define Role name and description.

Choose API permission scopes,

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.