"They belong to you!"
Translation:הם שייכים לכם!
There's nothing wrong with what you wrote. You are saying, "They belong to you" where "you" is singular. Their answer was a "you" that was plural. As we would say in the southern part of the U.S., "They belong to y'all." Or in some areas we would say, "They belong to you guys." It's too bad that English lost the distinction between singular and plural for "you." Singular used to be "thee" in the accusative or dative and "thou" in the nominative. You can still see this in the KJV Bible and others and some prayer books and hymns.
how to get tips and notes: (My favourite way): organized by skill in one pdf for the whole course: https://www.docdroid.net/JnfmyEV/tipsnotesbackup.pdf
Replace your username where USERNAME is for information on your progress & the tips & notes: https://duome.eu/USERNAME/progress
The whole course tips and notes are here (and the site has one for each Duolingo language): ,organized by skill individually: http://duolingo.wikia.com/wiki/Hebrew
You can also get them on the duolingo.com site (make sure your browser is in desktop view mode so you can see the other duolingo features like discussions & timed practice). From discussions you can search for all the discussions in this course (like this one you're reading, as well as see general duolingo discussions). If you can't see discussions on the main screen once logged into duolingo you're not in desktop view.