Server side validation of PayButton POST

BTCPayServer/Models/AppViewModels/PayButtonViewModel.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
 using System.Linq;
 using System.Threading.Tasks;
 
@@ -8,6 +9,7 @@ namespace BTCPayServer.Models.AppViewModels
     public class PayButtonViewModel
     {
         public decimal Price { get; set; }
+        [Required]
         public string Currency { get; set; }
         public string CheckoutDesc { get; set; }
         public string OrderId { get; set; }