bitwarden/src/Api/Models/Request/Accounts/TaxInfoUpdateRequestModel.cs

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace Bit.Api.Models.Request.Accounts
{
    public class TaxInfoUpdateRequestModel : IValidatableObject
    {
        [Required]
        public string Country { get; set; }
        public string PostalCode { get; set; }

        public virtual IEnumerable<ValidationResult> Validate (ValidationContext validationContext)
        {
            if (Country == "US" && string.IsNullOrWhiteSpace(PostalCode))
            {
                yield return new ValidationResult("Zip / postal code is required.",
                    new string[] { nameof(PostalCode) });
            }
        }
    }
}