Phil, I posed the question, "You are from what country?" I certainly think that should be accepted, since it uses every word correctly, & is a natural way for a customs official to ask, or even someone who did not hear where you just said you were from, but heard all of the rest of your sentence. I may flag that for Duo to consider. I think any Spanish speaker would've understood that immediately.
I thought the verb estar was used for locations.
Por ejemplo: Mi casa esta en Francia. O tambien, la fiesta esta en la sala.
Wouldn't a question about a country be locational and thus shouldn't it be "de que pais estas"? (Apologies for the lack of accents. I've no idea how to do them on an English qwerty keyboard and my google skills are lacking.)
It does look like you're paying attention, and the general rule is that estar is used to indicate the location of something. The two wrong branches you go down with this are: First, even though an event takes place at a given location, because that location is an inherent property of the event, we use ser to describe it. So, "La fiesta es en la sala" is correct, even though we say "Él está en la sala" for a person (or thing).
Second, even though a country is a location, the origin of a person or thing is again an inherent characteristic, so we use ser for this as well. "Él es de España", he is from Spain. "El juguete es de China", the toy is from China.
While I can see how you would think that de is from desde it isn't. Yes they both are used for 'of' and 'from' but not because they are the same root word. Here's an article that will help.