Adding user to Active Directory Group .net core: A referral was returned from the server

I'm building a .net core 3 website where I'm trying to add a user to an Active Directory security group. The below code works fine in my development environment but once it's deployed to IIS I receive:

System.DirectoryServices.DirectoryServicesCOMException (0x8007202B): A referral was returned from the server.

The error occurs at "group.Save();"

    using (PrincipalContext pc = new PrincipalContext(ContextType.Domain, "ad.xxx.com:389", 
    "DC=ad,DC=xxx,DC=com", svcAccountUsername, svcAccountPw))
    {
       GroupPrincipal group = GroupPrincipal.FindByIdentity(pc, IdentityType.SamAccountName, groupName);
       group.Members.Add(pc, IdentityType.SamAccountName, username);
       group.Save();
    }

Again, this works locally in my development environment but not once deployed to IIS. Any suggestions on how to fix?

I would suggest looking up the account that you are trying to add to the AD. Other things i can suggest is using the debugger to confirm the account / group exists in the domain that you are running this under.

using (PrincipalContext pc = new PrincipalContext(ContextType.Domain, "domain" ...))
    {
       GroupPrincipal group = GroupPrincipal.FindByIdentity(pc, IdentityType.SamAccountName, groupName);
       // Do some validation / logging to make sure there is a group returned.

       var principal = Principal.FindByIdentity(pc, IdentityType.SamAccountName, username);
       // Do some validation here to make sure principal is not null

       group.Members.Add(principal);
       group.Save();
    }

Make sure the server running this script has access to the domain you are updating.