Display Server Side Model Validation Error message in View in ASP.Net MVC

 I want that the user should not enter more than 4 places of decimal value in the field and i want it to be server side validation. But the error is not coming when i am trying to validate it.

    public class LandDetailController : Controller
    {
        
        // GET: LandDetail
        public ActionResult Index()
        {
            CPSE_Landdetails cs = new CPSE_Landdetails();
            cs.PsuList = GetPsu();
            return View(cs);
        }

        [HttpPost]
        public ActionResult Index(CPSE_Landdetails cs)
        {
            if(!string.IsNullOrEmpty(cs.LandFreeHold))
            {
                string landfree = @"^[0-9]+(\.[0-9]{1,2})$";
                Regex re = new Regex(landfree);
                if (!re.IsMatch(cs.LandFreeHold))
                {
                    ModelState.AddModelError("LandFreeHold","Land Entry Not Valid");
                }
            }

            return View();
        }

        private List<SelectListItem> GetPsu()
        {
            string userid = Session["UserID"].ToString();
            string str = ConfigurationManager.ConnectionStrings["Con"].ConnectionString;
            List<SelectListItem> List = new List<SelectListItem>();
            using (SqlConnection con = new SqlConnection(str))
            {
                string query = "select Section_PSU from [CPSEdb].[dbo].[SectionMaster1] where [Section_name]='"+userid.ToString()+"'";
                using (SqlCommand cmd = new SqlCommand(query))
                {
                    cmd.Connection = con;
                    con.Open();
                    using (SqlDataReader rd = cmd.ExecuteReader())
                    {
                        while (rd.Read())
                        {
                            List.Add(new SelectListItem
                            {
                                Text = rd["Section_PSU"].ToString(),
                                Value = rd["Section_PSU"].ToString()

                            });
                        }
                    }
                    con.Close();
                }
            }
            return List;
        }
    }

<div class="container" style="margin-top:20px">
    @using (Html.BeginForm("Index", "Home", FormMethod.Post))
    {
        if (!@ViewData.ModelState.IsValid)
        {
            <span class="field-validation-error">@ViewData.ModelState["LandFreeHold"].Errors[0].ErrorMessage</span>
        }
        <div class="card">
            <div class="card-header">
                <table width="1024">
                    <tr>
                        <td valign="bottom"><label>Choose PSU</label></td>
                        <td>
                            @Html.DropDownListFor(model => model.CPSE_id, Model.PsuList, "-- Choose PSU --", new { @class = "form-control", required = "required" })
                        </td>
                    </tr>
                </table>
            </div>
        </div>
        <div class="card" style="margin-top:20px">
            <div class="card-header alert-danger">
                <label>Land Details</label>
            </div>
            <div class="card-body">
                <table width="1024">                    
                    <tr>
                        <td valign="bottom">
                            <label>Land Free Hold Other</label>
                        </td>
                        <td>
                            @Html.TextBoxFor(model => model.LandFreeHole_Other, new { @class = "form-control", required = "required" })
                        </td>
                        <td valign="bottom">
                            <label style="margin-left:30px">Land Free Hold Unit</label>
                        </td>
                        <td>
                            @Html.TextBoxFor(model => model.LandFreeHold_unit, new { @class = "form-control", required = "required" })
                        </td>
                    </tr>                    
                </table>
            </div>
        </div>
        <div style="text-align:center;margin-top:20px">
            <input type="submit" value="Submit Information" class="btn btn-primary" />
        </div>
    }

    @Scripts.Render("~/bundles/jquery")
    @Scripts.Render("~/bundles/jqueryval")
</div>