Can send max invoice value for lightning payments

BTCPayServer/JsonConverters/CurrencyValueJsonConverter.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using System.Reflection;
+using Newtonsoft.Json;
+using NBitcoin.JsonConverters;
+
+namespace BTCPayServer.JsonConverters
+{
+    public class CurrencyValueJsonConverter : JsonConverter
+    {
+        public override bool CanConvert(Type objectType)
+        {
+            return typeof(CurrencyValue).GetTypeInfo().IsAssignableFrom(objectType.GetTypeInfo());
+        }
+
+        Type longType = typeof(long).GetTypeInfo();
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            try
+            {
+                return reader.TokenType == JsonToken.Null ? null :
+                       CurrencyValue.TryParse((string)reader.Value, out var result) ? result :
+                       throw new JsonObjectException("Invalid Currency value", reader);
+            }
+            catch (InvalidCastException)
+            {
+                throw new JsonObjectException("Invalid Currency value", reader);
+            }
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            if(value != null)
+                writer.WriteValue(value.ToString());
+        }
+    }
+}