I was struggling trying to get the app to login without much success. If you’re facing a similar issue, it’s possible to login into the instance via your preferred browser, ideally one that respects your privacy, and go to Options (usually the little three dots on the upper right corner of your screen), from there you can tap “Add to Home Screen” or “Install” and it will create a shortcut that can be accessed as an app (identically). Hope this helps, hasta la victoria!