Android CORS issue when using fetch

I just started a new project, in which I am reusing a component I used earlier in another Ionic v3 project. No modifications were done to the code.

The “fetch” simply gets a json from a server (not mine, operator ftp server), and my previous project can fetch that json without problem. Now the same code, used in a new project, is throwing a CORS error whenever I deploy my test app to Android.

Any clues as to what might be going wrong?

The only plugin I saw, which might have an effect on the fetch, is cordova-plugin-ionic-webview 3.1.1

Part of the code:

await fetch(CHANNELSURL, {
      method: 'GET',
      headers: {
        'Accept': 'application/json, text/plain',
        'Content-Type': 'application/json, text/plain',
        'Cache-Control': 'no-cache',
        'Save-Data': 'off',
        'Connection': 'close'
      }
    })
    .then(response => {
      return response.json();
    })