Why duollingo does not understand what I say? This is a possible reason...

When you are practicing, set Microphone Boost to zero.

I did this, and rarely duolingo says it does not understand what I say.

Well, of course we must not forget the other reason duolingo does not uderstand what you say is because your pronunciation is wrong.

I hope this helps you.

I'm currently finishing he Italian course. What about you?