Using the sdf plugin for webstorm, but I'm trying to add our new sandbox via browser based, but I keep getting the error

Address already in use: bind

I've already got 3 accounts, so I don't know what its issue is with adding this new one

When you start browser authentication, the plugin starts listening on port 52300 for the end of the authentication process. If this port is already in use, it can't listen on the process. I would try restarting WebStorm. If that doesn't work, try to find what else is listening on that port, or restart your computer.