DAW audio sharing is not compatible with ASIO4ALL .
If the Sessions plugin is not visible in your DAW, make sure to scan the default plugin folder.
If you can't hear one collaborator in particular, hover over the 3 dots in the top right-hand corner of their screen and verify their volume level.
If you are unable to see the other participants’ video, go into your settings in the bottom right-hand corner (3 dots) and change your video quality to 'Standard'.
Due to a limitation with REAPER on macOS, the space bar unfortunately does not add the space entry, but instead will do the start-stop command from DAW. The workaround is to remove that shortcut in REAPER's preferences.