"I have learned that from you."
Translation:Ich habe das von dir gelernt.
The informal pronouns "du/dich/deine/deinem/deinen/ihr/euch/eure/euren" (I might have forgotten one) can be capitalized optionally if you are addressing someone in a letter. The formal pronouns "Sie, Ihre" etc. have to be capitalized if you are addressing someone in a letter. Since there is no context given, Duolingo is just plain wrong.
I see that the "keyed response" in the lesson here differs from the one given here. In the lesson, "dir" was replaced with "Euch" - capitalized.
I see that others have suggested that the familiar pronouns can be capitalized, fair enough.
Nevertheless, "euch" is "you" plural; did Duo make a mistake here, thinking to invoke the dative of "Sie" (which would have been "Ihnen")?