Puma and Puma Dev Linux issue

[resistorsoftware]

I am using Linux and have Puma setup such that my Rails App works when I call it with something.test on my laptop. I have a MacOS machine running same setup. If I open an ngrok tunnel to http://localhost:3206 I can see on my MacOS machine that everything works! So if I start an ngrok tunnel from foo.com to my http://localhost:3206, not only does my MacOS machine with Puma Dev and Puma work, but... like magic, because we are on the same wifi network, if I access the same website on my laptop running Linux, it too all works! So I am so close to glory.

If however, if I start the tunnel on the Linux machine, and then foreman tries to bring up the Puma rails web server, it is blocked! I get this message from Puma!

/home/dlazar/.rbenv/versions/3
.2.2/lib/ruby/gems/3.2.0/gems/puma-6.3.0/lib/puma/binder.rb:334:in `initialize':
Address already in use - bind(2) for "127.0.0.1" port 3206 (Errno::EADDRINUSE)

I am not sure why the Linux setup has a problem MacOS does not exhibit. This is my last blocker to getting Puma Dev style tunneled development (with ngrok) working. Can anyone help me to try and debug this issue with Linux and Puma?

I have a sneaking suspicion this is an NGrok problem, since when I start it on MacOS, the Linux box works fine, but when I start the tunnels on Linux, Puma cannot start... am I right? Anyone familiar with this?