Question

Is there a way to access validation error messages in the controller. I’m not finding them anywhere in ModelState.

Answer 1

Iterating over ModelState is used for this purpose.
Something along these lines:

if (!ModelState.IsValid)
{
    StringBuilder result = new StringBuilder();

    foreach (var item in ModelState)
    {
        string key = item.Key;
        var errors = item.Value.Errors;

        foreach (var error in errors)
        {
            result.Append(key + " " + error.ErrorMessage);
        }
    }

    TempData["Errors"] = result.ToString();
}