In Fluenz 4 session 12 exercise "write what you read" I translated "I asked my parents for a book" as "J'ai demandé mes parents pour un livre" but was not accepted as correct. However, when I switched the position of the objects as in "J'ai demandé un livre à mes parents" then it was accepted.

Can someone provide little clarification why my first attempt was incorrect? Also why à and not pour?