"Antwort" is feminine, so you add -e to "ihr" to gain correct nominative object.
But I would like to know why I got an error on "What is your answer?", as "Ihr" also is the formal form for "your"?
so we can say that whenever Ihr is used instead of ihr, that means formal You is meant?
I think it's because the lower case letter. "what is your answer" = Was ist Ihre Antwort? (Sie-formal) Was ist deine Antwort? (Du-Informal)
But it says in the menu of possible meanings when you put your mouse over it that it can mean her, their, or your. So it is not fair that your is not a valid answer. It makes more sense to explain the distinction when we learn about formal you, or to teach the menu about capitalization
That would be "how is your answer?", which kind of makes sense in English but would be unusual, and I don't think it works at all in German.
I just ask because that it what I learnt as a German native speaker.
I've checked the numbers on Google. "Was ist deine / Ihre Antwort" is much more common; a search yields about three times more results than "Wie ist deine / Ihre Antwort". I'm surprised.
My girlfriend tells me it is a regional thing. I wouldn't know TBH.
Interesting! My German also has lots of dialect bits that I haven't learned aren't the usual way to say things, so I know the feeling.
"What is YOUR answer" should be accepted as an answer indicating formal speech.
To write "Ihre" in capital letters is only required in a formal address, like a letter, etc.
You misinterpreted that article. It only mentions the informal 2nd person singular pronoun (du) and the informal 2nd person plural pronoun (ihr). The formal 2nd person pronoun (Sie) always has to be capitalised. The same applies to their respective possessive determiners. Make sure you don't confuse the informal 2nd person plural pronoun (ihr) with the formal 2nd person possessive determiner (Ihr).
"Die Formen des Anredepronomens Sie schreibt man immer und überall groß und auch die Formen des entsprechenden Possessivpronomens, d. h. auch in der wörtlichen Rede im Prosatext: Welche Schlussfolgerungen ziehen Sie daraus? Solche, die ich Ihnen nicht auf die Nase binden will (Willi Achten: Die florentinische Krankheit). "
I'm not entirely sure what you mean. There are no exceptions, and there's no distinction between singular and plural when it comes to the formal you.