"Tell me what you have done."
Translation:Dimmi cos'hai fatto.
They don't know Italian, I wrote "dimmi che hai fatto" and it's wrong... another time I wrote "dimmi cosa hai fatto" and DL said I had a typo in my answer, probably in his brain there is a bug... their dictionary has too few words... they can't teach Italian... probably other languages, but not Italian. Che/cosa/che cosa... all of them are correct, but you'll get error, just report it. Anyway it can't be possible translating literally, it doesn't work. Frustrating....
Dimmi che hai fatto and Dimmi cosa hai fatto are fully legit, although the most common answer would likely be Dimmi cos'hai fatto.
You can report this. Hopefully, a contributor will add the alternative forms to the database of correct answers.