Installed the app. Doesn't use the My Mazda login, so went to sign up for an account - my phone country code (UK) is not listed so I can't specify my phone number. I guess that means the app doesn't work in the UK, which is an odd way of telling me.

 

You're right, the account must be different from the one used for the MyMazda app.
Have you checked the Mazda UK website?
The Mazda France website specifies "European Union".

 

Any other developer would put an App Store restriction in place - i.e. I wouldn't be able to see it for my country. They appear to have made it available for all but then surprise you during the set-up. That's a pretty poor experience.

 

I just gave a quick look at this app and it is really expensive, at least here in Slovenia.
Better use local apps or there are other roaming apps (Electroverse, Ionity, etc.).
I have not registered, so maybe there are some cheaper plans inside the apps.