Charles proxy to connect to localhost from SSL App

Question

Overview:

• I have a Android App that points to some remote https server
• I have a Rails app on localhost:3000
• I want to direct trafic from the app to my localhost

Details:

1. My machine IP is 192.168.0.16
2. I have Charles Proxy setup on port 8888
3. On the Android phone I have configured the Wifi connection to have a manual proxy to 192.168.0.16:8888
4. On the Android phone I have installed the SSL root cert via chls.pro/ssl, added to VPN and apps (as per https://stackoverflow.com/a/33113392/119790)
5. Charles->Access Control Settings has my Android IP 192.168.0.15 listed
6. Charles->SSL Proxying Settings has location: *remoteserver.com:443
7. Charles->Map Remote
   • from: https, my.remoteserver.com, 443
   • to: http, localhost, 3000
8. When I use the app Charles shows Status: Connected to remote host, and nothing more

9. On my localhost I have a rails server

   $ rails server
   ...
   Listening on localhost:3000, CTRL+C to stop
   

10. When I use the app nothing is ever logged (I can curl localhost and it logs that)
11. If I stop the Rails server then Charles shows Status: Failure, Response code: 503 Error
12. So it connects, but fails to get a response?

rails server running

rails server not running

System:

• Android v7.1.2
• Charles v4.2.1
• OSX v10.13.3