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 Settings at the upper right
Click Audio at the top
In the Voice Chat section, ensure that Voice Chat Output Device (where you want to hear incoming voice chat) and your Voice Chat Mic Device (what you will use for your outgoing voice) are set to your correct devices.
Also, make sure that Voice Chat Audio is set to On.
We have also heard that 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