OneSignalClient.cs

public class OneSignalClient : MonoBehaviour {
    void Start() {
        InitOneSignal();
    }

    public void InitOneSignal() {

        OneSignal.SetLogLevel(OneSignal.LOG_LEVEL.VERBOSE, OneSignal.LOG_LEVEL.NONE);

        OneSignal.StartInit(ClientConfig.oneSignalAppId)
            .HandleNotificationOpened(HandleNotificationOpened)
            .EndInit();
        
        OneSignal.SetLocationShared(false);

        OneSignal.inFocusDisplayType = OneSignal.OSInFocusDisplayOption.Notification;
    }

    public static void HandleNotificationOpened(OSNotificationOpenedResult result) {
        string extraData = JsonConvert.SerializeObject(result.notification.payload.additionalData);
        
        Debug.Log($"Handled notification. Extra data: {extraData}\naction id: {result.action.actionID}");
        Debug.Log(
            $"Images used: largeIcon:{result.notification.payload.largeIcon}\nbigPicture:{result.notification.payload.bigPicture}");
    }
}