title: Error:"The user doesn't exist or is not unique" in sharepoint Adding user using CSOM
body: <p>I'm trying to Add a User to the SharePoint site using CSOM but I'm getting an stating 'The user does not exist or is not unique' is there something wrong with my LoginName?. "anil@developer19.onmicrosoft.com" is an active user in the Organization.</p>
  
  <pre><code>using System;
  using System.Security;
  using Microsoft.Online.SharePoint.TenantAdministration;
  using Microsoft.SharePoint.Client;
  namespace CreateSiteCollections
  {
      class Program
      {
          static void Main(string[] args)
          {
             //Opens the Admin URL 
              using (ClientContext ctx1 = new ClientContext("https://developer19.sharepoint.com/sites/codesite"))
              {
                  //Authenticating with Tenant Admin
                  SecureString passWord = new SecureString();
                  foreach (char c in "Password".ToCharArray())
                      passWord.AppendChar(c);
                  ctx1.Credentials = new SharePointOnlineCredentials("kailash@developer19.onmicrosoft.com", passWord);
                          GroupCollection cg = ctx1.Web.SiteGroups;
                          Group oGroup = cg.GetById(14);
  
                          UserCreationInformation user = new UserCreationInformation();
                          user.Email = "anil@developer19.onmicrosoft.com";
                          user.LoginName = "developer19/anil";
                          user.Title = "Anil";
                          User oUser = oGroup.Users.Add(user);
                          ctx1.ExecuteQuery();
              }
        }
     }
  }
  </code></pre>