Either ErrorMessageString or ErrorMessageResourceName must be set, but not both error using CreditCardAttribute

Question

This is my model:

namespace MvcApplication2.Models
{
    public class CreditCard
    {
        [CreditCard(ErrorMessageResourceType = typeof(Messages), Error         


        

Answer 1

In my case, I was using ErrorMessage as "" in .Net Core 3.1 API.

[Required]
[RegularExpression("^[1-9]\\d*$", ErrorMessage ="")]
public int fieldName { get; set; }

I change to ErrorMessage ="Invalid Value Or some other message" and the issue is solved.