Make sure model binder error are returning error 422, use DateTimeOffsetModelBinder

BTCPayServer/ModelBinders/DateTimeOffsetModelBinder.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Reflection;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc.ModelBinding;
+using Microsoft.VisualBasic.CompilerServices;
+
+namespace BTCPayServer.ModelBinders
+{
+    public class DateTimeOffsetModelBinder : IModelBinder
+    {
+        public Task BindModelAsync(ModelBindingContext bindingContext)
+        {
+            if (!typeof(DateTimeOffset).GetTypeInfo().IsAssignableFrom(bindingContext.ModelType) &&
+                !typeof(DateTimeOffset?).GetTypeInfo().IsAssignableFrom(bindingContext.ModelType))
+            {
+                return Task.CompletedTask;
+            }
+            ValueProviderResult val = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
+            if (val == null)
+            {
+                return Task.CompletedTask;
+            }
+
+            string v = val.FirstValue as string;
+            if (v == null)
+            {
+                return Task.CompletedTask;
+            }
+
+            try
+            {
+                var sec = long.Parse(v, CultureInfo.InvariantCulture);
+                bindingContext.Result = ModelBindingResult.Success(NBitcoin.Utils.UnixTimeToDateTime(sec));
+            }
+            catch
+            {
+                bindingContext.Result = ModelBindingResult.Failed();
+                bindingContext.ModelState.AddModelError(bindingContext.ModelName, "Invalid unix timestamp");
+            }
+            return Task.CompletedTask;
+        }
+    }
+}