You may see this error message "Can't record due to a problem with the microphone"
This error usually indicates another app on the device has control of the microphone and is not releasing it properly to Zello. Try deleting or turning off any apps using the microphone and retry Zello.
The "Hey Cortana" feature is known to have a bug which results in this error even if Cortana is not open and being used. To resolve this, turn "Hey Cortana" off on your Android device.