Some Macs have exhibited microphone issues after upgrading to Mac OS X Mojave.
This is caused by faulty permissions associated with a new Mac security feature governing microphones specifically.
If an app is detected to require access to use the microphone, your OS will ask for permission to allow the application to access the microphone. This will happen for each application that needs access to the microphone, even if that application had already been used on your computer, prior to the upgrade.
This error is characterised by an inability to speak and may also include a grayed-out microphone icon in the lower-left corner, even when a known-good microphone is plugged in.
The solution to this problem is to go to Settings, then click on the Security & Privacy icon.
In the next window, first of all click on the 'Privacy' tab, then make sure you scroll down on the list that is on the left until you mind the option 'Microphone', click that option and finally, look for ConnectWorld on the right side.
To grant the app permission to access the microphone, check the box to the left.
If ConnectWorld is open when you click the checkbox, changes to the microphone permissions will not be applied until you close it. A notification window will pop up, giving you the option to close it immediately. Once you have made the changes here, click the lock icon to prevent further changes.
NOTE: If ConnectWorld is already checked, uncheck, and re-check the box, then restart the app.