Can't share site with users even when I have "Full Control"

Question

I am creating sites dynamically using CSOM in C#.

Part of this process is creating 2 groups, Members and Owners, which have permission levels Contribute and Full Control respectively:

I am in the Owners group, so I should have Full Control, but when i try to invite another user to that group I am denied that access:

in fact I also get the same when trying to invite the user to the Members group.

Why? What does "Full Control" even mean if I can't invite people to these groups?

I also noticed that if I go into the Members group it says I don't have permission to view the membership... What is the point in having full control if it doesn't give me full control?

Answer 1

I had to set the group owner, and I did it with this code

public void SetGroupOwner(string groupName, string ownerGroupName)
{
    using (var clientContext = new ClientContext(baseUrl))
    {
        clientContext.Credentials = credentials;
        var web = clientContext.Web;

        var group = web.SiteGroups.GetByName(groupName);
        var groupOwner = web.SiteGroups.GetByName(ownerGroupName);

        group.Owner = groupOwner;
        group.Update();
        clientContext.ExecuteQuery();
    }
}

So I set the owner of both groups to CRMT_TESTWS34 Owners, meaning that the owners group is owned by itself.

It now seems to work fine.