Add a user to a Discourse group using RestSharp

AddToDiscourseGroup.cs

private bool setGroupAccess(string username, string groupName)
{
    string url = "/groups/{group_name}.json?api_key={api_key}&api_username={api_username}";
    var client = new RestClient(ConfigurationManager.AppSettings["DiscourseUrl"]);
    var request = new RestRequest(url, Method.GET);
    request.AddUrlSegment("group_name", groupName);
    request.AddUrlSegment("api_key", ConfigurationManager.AppSettings["DiscourseAPIKey"]);
    request.AddUrlSegment("api_username", ConfigurationManager.AppSettings["DiscourseAPIUsername"]);
    request.RootElement = "basic_group";
    IRestResponse<DiscourseGroup> groupInfoResponse = client.Execute<DiscourseGroup>(request);
    int groupId = groupInfoResponse.Data.id;                
    
    url = "/groups/{group_name}/members.json?api_key={api_key}&api_username={api_username}";
    client = new RestClient(ConfigurationManager.AppSettings["DiscourseUrl"]);
    request = new RestRequest(url, Method.GET);
    request.AddUrlSegment("group_name", groupName);
    request.AddUrlSegment("api_key", ConfigurationManager.AppSettings["DiscourseAPIKey"]);
    request.AddUrlSegment("api_username", ConfigurationManager.AppSettings["DiscourseAPIUsername"]); 
    IRestResponse<List<DiscourseGroupUserEntry>> response = client.Execute<List<DiscourseGroupUserEntry>>(request);
    if (response.StatusCode == HttpStatusCode.OK && response.Data != null)
    {
        List<string> usernames = response.Data.Select(c => c.username).ToList();
        if (!usernames.Contains(username))
        {
            usernames.Add(username);
            string usernameString = string.Join(",", usernames);
            url = "/admin/groups/{group_id}?api_key={api_key}&api_username={api_username}";
            request = new RestRequest(url, Method.PUT);
            request.AddUrlSegment("group_id", groupId.ToString());
            request.AddUrlSegment("api_key", ConfigurationManager.AppSettings["DiscourseAPIKey"]);
            request.AddUrlSegment("api_username", ConfigurationManager.AppSettings["DiscourseAPIUsername"]);
            request.AddParameter("group[name]", groupName);
            request.AddParameter("group[alias_level]", "0");
            request.AddParameter("group[usernames]", usernameString);

            IRestResponse putResponse = client.Execute(request);
            return response.StatusCode == HttpStatusCode.OK;
        }
        //already in the group
        return true;
    }
    return false;
}

DiscourseGroupEntry.cs

public class DiscourseGroupUserEntry
{
    public string id { get; set; }
    public string avatar_template { get; set; }
    public string last_seen_at { get; set; }
    public string name { get; set; }
    public string username { get; set; }
}