Error handling

*** Models/MonthEnum.cs ***
public enum MonthEnum : int
{
    January = 0,
    February,
    March,
    April,
    May,
    June,
    July,
    August,
    September,
    October,
    November,
    December
}

*** Models/MonthEnum.cs ***
[HttpPost]
public IActionResult Index(PersonalData personalData)
{
    if (!ModelState.IsValid)
        return View(personalData);

    var monthOfBirth = (MonthEnum)personalData.DateOfBirth.Month;
    var shortMonth = monthOfBirth.ToString().Substring(0, 3);

    TempData["personName"] = personalData.FirstName + " " + personalData.LastName;
    TempData["personBirthMonth"] = shortMonth;

    return RedirectToAction("Success");
}

*** Success.cshtml ***
@{
    var personName = TempData["personName"] as string;
    var personBirthMonth = TempData["personBirthMonth"] as string;
}

<h1>You have succesfully submitted the data</h1>
<hr />
<div class="text-primary">Name: @personName</div>
<div class="text-primary">Month of birth: @personBirthMonth</div>
<hr />
<a asp-controller="Home" asp-action="Index" class="btn-sm btn-primary">Back</a>