I can hear others, but others say they can't hear me?

Please make sure that you have the in SIM Sound Options...

To do this, launch a session (a Test session for example).

Click Options

Click the Sound tab at the bottom

In the Voice Chat section, please make sure that your Mic option is set to your microphone.

Also make sure that Enable Voice Chat is checked.

We have also heard many have this issue after doing a Windows update. If this is the case, please see:  https://answers.microsoft.com/en-us/windows/forum/windows_10-hardware/windows-10-update-1803-disabled-microphone-input/a6449ccb-23a7-4972-8315-b5996060a987