Add Extension using SharePoint CSOM

private string appJsonInfo;
private AppDeclaration Apps;

// A class to hold JSON converted objects for Apps
private class AppDeclaration
{
    public string appName;
    public string appId;
    public string clientsideId;
}

// Declare and create a Json Object for all Apps
public void DeclareAppIds
{
  appJsonInfo = "[{appId: \"xxxxx-xxxx-xxxx-xxxx-xxxxxxxx\", appName: \"testApp\", clientsideId: \"xxxxxx-xxxx-xxxx-xxxx-xxxxxxxx\"}, " +
                                      "{appId: \"xxxxxx-xxxx-xxxx-xxxx-xxxxxxxxx\", appName: \"testApp1\", clientsideId: \"xxxxxx-xxxx-xxxx-xxxxx-xxxxxx\"}, " +
                                      "{appId: \"xxxxxx-xxxx-xxxx-xxxx-xxxxxxxxx\", appName: \"testApp2\", clientsideId: \"xxxxxx-xxxx-xxxx-xxxxx-xxxxxx\"}]";
                                      
  Apps = JsonConvert.DeserializeObject<List<AppDeclaration>>(appJsonInfo);
}

public void AddExtensions(string listURL)
{
    AppDeclaration App = appConfiguration.Apps.Find(app => app.appName.Contains("<app name>"));
    Guid AppID = new Guid(App.clientsideId);
    string AppName = App.appName;

    using (ClientContext context = new ClientContext(<siteUrl>))
    {
        if (AppID != Guid.Empty)
        {
            context.Credentials = new SharePointOnlineCredentials(UserName, SecurePass);
            List list = context.Web.GetListByUrl(<list URL>);
            log.Info("Finding and Adding Extenstion to " + list.Title);
            context.Load(list);
            context.Load(list, t => t.UserCustomActions);
            context.ExecuteQuery();

            UserCustomActionCollection listExt = list.UserCustomActions;
            bool AppPresent = false;

            foreach (UserCustomAction customAcc in listExt)
            {
                if (customAcc.ClientSideComponentId == AppID)
                {
                    tenancyAppPresent = true;
                    continue;
                }
            }

            if (!tenancyAppPresent)
            {
                UserCustomAction customAction = list.UserCustomActions.Add();
                customAction.ClientSideComponentId = AppID;
                customAction.Location = "ClientSideExtension.ListViewCommandSet";
                customAction.Name = AppName;
                customAction.Title = AppName;
                customAction.Update();
                context.ExecuteQuery();
            }
        }
        else
            throw new Exception("System Error - App cannot be added as no App ID found");
    }
}