Laravel PWA - use in offline mode for Safari on Iphone & Ipad

Question

I created a webplatform for a client in Laravel 9. Everything is working perfect but he wants to use it offline as well. I installed the package for Laravel PWA. On a Windows desktop Chrome it is working fine (offline as well).

But my client is using the platform on Iphone and Ipad, so Safari. There I can create the PWA and use it. Unfortunately it does not work offline. I'm getting the following error:

Fetch event respondwith received an error

I tried to solve it but I don't have much experience with these kind of workers.

This is the package I used: https://packagist.org/packages/ladumor/laravel-pwa

I think the problem is in the sw.js file:

const preLoad = function () {
    return caches.open("offline").then(function (cache) {
        // caching index and important routes
        return cache.addAll(filesToCache);
    });
};

self.addEventListener("install", function (event) {
    event.waitUntil(preLoad());
});

const filesToCache = [
    '/',
    '/offline.html'
];

const checkResponse = function (request) {
    return new Promise(function (fulfill, reject) {
        fetch(request).then(function (response) {
            if (response.status !== 404) {
                fulfill(response);
            } else {
                reject();
            }
        }, reject);
    });
};

const addToCache = function (request) {
    return caches.open("offline").then(function (cache) {
        return fetch(request).then(function (response) {
            return cache.put(request, response);
        });
    });
};

const returnFromCache = function (request) {
    return caches.open("offline").then(function (cache) {
        return cache.match(request).then(function (matching) {
            if (!matching || matching.status === 404) {
                return cache.match("offline.html");
            } else {
                return matching;
            }
        });
    });
};

self.addEventListener("fetch", function (event) {
    event.respondWith(checkResponse(event.request).catch(function () {
        return returnFromCache(event.request);
    }));
    if(!event.request.url.startsWith('http')){
        event.waitUntil(addToCache(event.request));
    }
});