Are you using the current version of the League Dominator mobile app? The previous versions will no longer work for this year, so you will need to use the 2024 mobile app version.
If you have a Footballguys Premium subscription, access to the League Dominator Mobile App and League Dominator Online on the website are part of the subscription.
You can use League Dominator online on your mobile device. It's not a mobile app, it's viewable on your mobile devices on your web browser.