public class User
{
    public string Id { get; protected set; }
    public Credential Credential { get; protected set; }
    // unrelated properties and methods omitted for simplicity
}

public sealed class Credential: ValueObject<Credential>
{
    public string Email { get; private set; }
    public string UserName { get; private set; }
    public string Password { get; private set; }
    public string SecurityStamp { get; private set; }

    public Credential() { }

    public Credential(string email, string userName, string password, string securityStamp)
    {
        Email = email;
        UserName = userName;
        Password = password;
        SecurityStamp = securityStamp;
    }

public class CoreContext: DbContext
{
    public IDbSet<User> Users { get; set; }

    public CoreContext(string connectionString) : base(connectionString) {}

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        Database.SetInitializer<CoreContext>(null);

        modelBuilder.ComplexType<Credential>().Property(ucr => ucr.Email).HasColumnName("Email");
        modelBuilder.ComplexType<Credential>().Property(ucr => ucr.UserName).HasColumnName("UserName");
        modelBuilder.ComplexType<Credential>().Property(ucr => ucr.Password).HasColumnName("Password");
        modelBuilder.ComplexType<Credential>().Property(ucr => ucr.SecurityStamp).HasColumnName("SecurityStamp");

        modelBuilder.Entity<User>().Property(u => u.Credential.Email).HasColumnName("Email");
        modelBuilder.Entity<User>().Property(u => u.Credential.UserName).HasColumnName("UserName");
        modelBuilder.Entity<User>().Property(u => u.Credential.Password).HasColumnName("Password");
        modelBuilder.Entity<User>().Property(u => u.Credential.SecurityStamp).HasColumnName("SecurityStamp");
    }
}

The 'Credential.Email' property does not exist or is not mapped for the type 'User'.