Dartfish Express stand alone has been removed from the Google Play store in June 2022 and from the Apple App store in January 2023. This app is not supported anymore.
You should still have the installer in your Apple / Google Play account under which the app was purchased.
Please note that this app has been replaced by myDartfish Express included in myDartfish Mobile : https://www.dartfish.com/mobile and in all the myDartfish subscriptions.