Enable External Domain in SPO

DomainEnableSPO

Tenant tenant = new Tenant(_context);
                SPOSitePropertiesEnumerable prop = null;
                prop = tenant.GetSiteProperties(0, true);
                _context.Load(prop);
                _context.ExecuteQuery();

                foreach (SiteProperties sp in prop)
                {
                    try
                    {
                        var site_cxt = new ClientContext(sp.Url);
                        site_cxt.Credentials = sp.Context.Credentials;
                        var web = site_cxt.Web;
                        var site = site_cxt.Site;
                        site_cxt.Load(web, w => w.SiteUsers);
                        site_cxt.Load(site);
                        site_cxt.ExecuteQuery();

                        ScriptSafeDomainEntityData ssded = new ScriptSafeDomainEntityData();
                        ssded.DomainName = ("http://External-Domain-to-be-added-to-spo");
                        site.CustomScriptSafeDomains.Create(ssded);
                        site_cxt.ExecuteQueryRetry();
                        Console.WriteLine("  **** External-Domain added to the site  **** " + " : " + sp.Url + "");
                        strbldr.AppendLine("  ****  External-Domain added to the site **** " + " : " + sp.Url + "");

                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine("---- Exception --- * *" + sp.Url + " - " + ex.Message);
                        strbldr.AppendLine(" ---- Exception --- * *" + sp.Url + " - " + ex.Message);
                    }
                }