An example of an JsonConverter that converts a Flags enum to an string[]. Also converters string[] and int[] back to Flags enum type. Supports generic types

Flags Enum to String array Json Converter

public class FlagsEnumToStringArrayJsonConverter<T> : JsonConverter
        where T: struct
    {
        public override bool CanConvert(Type objectType)
        {
            return objectType.IsEnum && objectType.GetCustomAttributes(typeof(FlagsAttribute), false).Length > 0;
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            if (reader.TokenType != JsonToken.StartArray)
                return null;

            var values = serializer.Deserialize<string[]>(reader).AsEnumerable();
            foreach (var item in values)
            {
                if (!Enum.TryParse<T>(item, ignoreCase: true, result: out var result))
                    return null;
            }

            return values
                 .Select(x => Enum.Parse(objectType, x, ignoreCase: true))
                 .Aggregate(0, (current, value) => current | (int)value);
        }

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            if (value == null)
            {
                writer.WriteNull();
                return;
            }

            var flagsStringArray = Enum.GetValues(value.GetType())
                 .Cast<int>()
                 .Where(intValue => (intValue & (int)value) == intValue)
                 .Select(intValue => Enum.ToObject(value.GetType(), intValue).ToString().ToLowerInvariant())
                 .ToArray();

            serializer.Serialize(writer, flagsStringArray);
        }
    }