Offline Leaflet Map not showing the map only grey color

So what am I doing is trying to get a map from a certain part and load it, it works with the browser and using ionic serve but when doing apk file (ionic build) and after installing the app it only shows grey color. I follow this tutorial to work in offline.

Below is my code ='map', { center: [8.48252667, 124.64722222], zoom: 16, trackResize: false});
leaflet.tileLayer('../assets/Northmin/{z}/{x}/{y}.png', {
attribution: 'Sample',
maxZoom: 16
leaflet.marker([8.48252667, 124.64722222], {
title: 'Marker', alt: 'marker', icon: leaflet.icon({
iconUrl: '../assets/imgs/bank.png',
iconSize: [38, 38],
iconAnchor: [22, 94],
popupAnchor: [-3, -76],
shadowSize: [68, 95],
shadowAnchor: [22, 94]

Is this the problem of loading the layer?

I’m experiencing the same problem.
Had you found a solution?