"What did you guys buy in that store?"
Translation:¿Qué compraron ustedes en esa tienda?
I just tried '¿Qué comprasteis en esa tienda?' (on the grounds that 'you guys' sounded informal), but DL objected… 'You used the vosotros/vosotras form "comprasteis" instead of the ellos/ellas/ustedes form "compraron". Am I confused or is DL?
Well, Duolingo says it teaches American English and Latin American Spanish.
However, it should still accept European Spanish answers. So your answer should be added to the database. To do that, you'll have to use the report button and check "my answer should be accepted."
In case you were wondering, although ustedes is used only for the formal you plural in parts of Spain, in Latin American Spanish it is also the familiar you plural.
¿Qué compraron, chicos, en esa tienda? was wrong. The "you" is implied in this answer. Hmmm...