Balena host server on internal localhost and reach it through balena VPN

Say I have a small gRPC server running on localhost:4321 and I want to send requests to this service from outside the balena VPN.

I can do the following

  1. Open a balena tunnel
  2. Port forward 4321 through that tunnel

But now whenever I try to send a request to it I get stuck at the TLS handshake. Is there a way to overcome this?