gRPC passthrough proxying with tyk

Well you are missing a couple of configurations. Version and auth mode

  "use_keyless": true,
  "version_data": {
    "not_versioned": true,
    "default_version": "",
    "versions": {
      "Default": {
        "name": "Default",
        "expires": "",
        "paths": {},
        "use_extended_paths": true,
        "extended_paths": {}
      }
    }
  }

But those are not the ones causing the issue. I see you have specified a listen path for your API. It should be the root path /

You also mentioned you are using docker. You may need to access localhost from the host inside the docker container.