Initially the test store was set for one country only, therefore I tried with allowing a second country. I also tried using shipping and billing addresses from different countries in case this would affect some default behavior.
Unfortunately after multiple different trials, the result is always the same; no billing country output.
I could of course get the country using the regionCode but this would be very inefficient knowing that the country should simply get passed with the other billing information.
I could of course use the default customer or shipping country but these could be different in the case where a customer would pay with a foreign credit card but still get delivered in the designated country.
There is so many variation cases to evaluate and bottom line:
We need this value to get passed as it should.
From my understanding, having taken a look into other default Magento payment modules as Authorizenet, it seems that all payment modules are using similar methods and would not be getting the country.
Magento version: 2.1.0
Extensions Installed: 3
Payment Extension Installed: 1 (Only this one)
I did not take the time to dig in the core code to see where the billing country does not get passed. Still this issue should be easy enough to resolve.