If you're seeing dollars, then you're probably using eurail.com. On interrail.eu, I only have the choice between euros and pounds.

My thanks for taking the time to respond …….

I downloaded the app in the Uk and it’s seems to be “gender neutral- i.e. had no idea if a com or eu……

The app can't book reservations. All it can do is forward to some of the websites where you can book, including the Interrail/Eurail website. Maybe for some reason it forwards to the Eurail website in your case. You should be able to change that by going to More > Settings > Change region.