Your microphone needs to be less than 5 feet away from a human voice for Ava to transcribe something. Check our guide on digital audio (computer, TV) or setting up Ava in other environments if you're not in this situation.
Your microphone icon should be BLUE. This means Ava is listening and ready to transcribe.
Make sure you have no other apps recording audio at the same time (e.g. voice recorder app).
If you speak but no words appear, still: check the Internet connection on your smartphone (3G-4G-LTE or Wifi) by opening the Internet browser and searching something.
If Internet seems to be working fine: check your microphone permissions your phone settings. Go to the list of all the apps, find "Ava", and look at the permissions granted to it. The microphone one needs to be enabled for Ava to transcribe from your phone.
If you're in a group conversation, try to mute all the other microphones but yours. If only then Ava will transcribe words, this might be a calibration problem (your microphone is way less sensitive than all the other participants' microphones). Message us so we can help you there.