public sealed class AndroidNotification
{
    public enum Priority
    {
        MIN,
        LOW,
        DEFAULT,
        HIGH,
        MAX,
    }

    public enum Visibility
    {
        PRIVATE,
        PUBLIC,
        SECRET,
    }

    [JsonProperty("title")]
    public string Title { get; set; }

    [JsonProperty("body")]
    public string Body { get; set; }

    [JsonProperty("icon")]
    public string Icon { get; set; }

    [JsonProperty("color")]
    public string Color { get; set; }

    [JsonProperty("sound")]
    public string Sound { get; set; }

    [JsonProperty("tag")]
    public string Tag { get; set; }

    [JsonProperty("image")]
    public string ImageUrl { get; set; }

    [JsonProperty("click_action")]
    public string ClickAction { get; set; }

    [JsonProperty("title_loc_key")]
    public string TitleLocKey { get; set; }

    [JsonProperty("title_loc_args")]
    public IEnumerable<string> TitleLocArgs { get; set; }

    [JsonProperty("body_loc_key")]
    public string BodyLocKey { get; set; }

    [JsonProperty("body_loc_args")]
    public IEnumerable<string> BodyLocArgs { get; set; }

    [JsonProperty("channel_id")]
    public string ChannelId { get; set; }

    [JsonProperty("ticker")]
    public string Ticker { get; set; }

    [JsonProperty("sticky")]
    public bool Sticky { get; set; }

    [JsonProperty("event_time")]
    public DateTime EventTimestamp { get; set; }

    [JsonProperty("local_only")]
    public bool LocalOnly { get; set; }

    [JsonProperty("priority")]
    public AndroidNotification.Priority? Priority { get; set; }

    [JsonProperty("vibrate_timings")]
    public long[] VibrateTimingsMillis { get; set; }

    [JsonProperty("default_vibrate_timings")]
    public bool DefaultVibrateTimings { get; set; }

    [JsonProperty("default_sound")]
    public bool DefaultSound { get; set; }

    [JsonProperty("light_settings")]
    public LightSettings LightSettings { get; set; }

    [JsonProperty("default_light_settings")]
    public bool DefaultLightSettings { get; set; }

    [JsonProperty("visibility")]
    public AndroidNotification.Visibility? Visibility { get; set; }

    [JsonProperty("notification_count")]
    public int? NotificationCount { get; set; }
}

// Add new class for LightSettings

public sealed class LightSettings
{
    [JsonProperty("color")]
    public string Color { get; set; }

    [JsonProperty("light_on_duration")]
    public long LightOnDurationMillis { get; set; }

    [JsonProperty("light_off_durtaion")]
    public long LightOffDurationMillis { get; set; }
}

Finally, when sending the payload would look like this:
{
     "notification": {
            "title_loc_key" : "NOTIFICATION_TITLE",
            "body_loc_key" : "NOTIFICATION_MESSAGE"
     },
     "priority": "high",
     "condition": "'general' in topics"
}