From one John to another...
I didn't call the REST HTTP endpoint directly, but when using the G Suite Directory API Client Library I needed to loop thru multiple pages to receive all results.
This is the pattern I used. It would be very similar for the G Suite Reseller API.
/// <summary>
/// List all Members in a Domain Group.
/// <param name="service">DirectoryService object (Google Directory API)</param>
/// <returns>Collection of Member emails</returns>
/// </summary>
public IEnumerable<string> ListGroupMembers(DirectoryService service)
{
// Set Group key (email address of the Group or id of the Group)
var groupKey = "email-for-google-group@domain-name.com";
// Define parameters of request (Group email)
MembersResource.ListRequest request = service.Members.List(groupKey);
// Sadly, this won't work
request.MaxResults = int.MaxValue;
// And the max page size of response is ONLY 200!
// So you have to check for the next page token
// and execute another request if there is one
do
{
// Get Members response for this Group
Members response = request.Execute();
// Return the emails in this response page
foreach (var member in response.MembersValue)
{
yield return member.Email;
}
// Get next page token
request.PageToken = response.NextPageToken;
// Continue loop if next page token is not null
} while (!string.IsNullOrEmpty(request.PageToken));
}