Ajax request not working

Hi, why using DateTime for ContactNo? is it a typo?

[Required(ErrorMessage = "Please Enter ContactNo")]
[RegularExpression(@"^\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$", ErrorMessage = "Entered phone format is not valid.")]
public DateTime ContactNo { get; set; }