I don't own an Apple TV box, but have you tried rebooting both your Router and Apple TV box by temporary unplugging the power for a minute.
Also make sure your Apple TV is set up to the correct region and you are using the correct Apple Store of your country (either UK or Republic of Ireland depending where you live) assuming there is a setting in the ATV box
If no luck and you have a smartphone with mobile internet data on it, try your smartphone has a temporary wifi hotspot when attempting to download NOW App.
Not being an Apple TV customer I can’t be much help, however the statement “Ask apps not to track” is something that I’ve been coming across on all newly installed apps on my iPhone.
Must be new privacy settings from Apple?
This looks like an issue with the latest update released today. After selecting Ask app not to track, you need to force quit the app (by double pressing the home/tv button and swiping the app up) and then re open it and it should work normally.
For some reason whenever the app is on the splash screen, if it is interrupted it freezes and you have to quit the app.