What's the most commonly used word used to mean invoice?
What's the difference in meaning between Rechnung and Faktur?
The most commonly used word for the english term "invoice" is:
The word "Faktur" is in my opinion kind of obsolete and barely ever used nowadays.
Reference 1: https://www.dict.cc/?s=invoice
I disagree with SteffPoints Answer regarding "Faktura". In business in general this is a very well known word, used in everyday language. But you need to distinguish:
Rechnung is mostly the paper / pdf / document that is sent to somebody.
Faktura is the process of creating that document.
Seeing that special meaning it is normal, that someone who has nothing to do with writing invoices does not know that meaning and thinks it is "barely used".
As I am not a native english speaker, I have no idea, if "invoice" really has both meanings in english, but if it has, then the translation for the different meanings are correct.