Docker of Gateway Bridge cannot see port 1883 of a broker (Windows 10)

I have an MQTT broker (mosquitto) running in Windows 10. It is tested and fully working on I have a Docker container of the Chirpstack Gateway Bridge. It attempts to connect to the broker through port 1883, but always fails. I should see it failing to connect in the log of the broker but nothing appears there. The same error occurs “connection refused” even when the broker is turned off. I suspect the container is not getting outside of itself to communicate with port 1883 on the host. Your thoughts?

PS C:\BRIDGE> docker compose up
[+] Running 1/0
 - Container bridge-lora-bridge-1  Created                                                                                                                      0.0s
Attaching to bridge-lora-bridge-1
bridge-lora-bridge-1  | INFO[0000] starting ChirpStack Gateway Bridge            docs="" version=
bridge-lora-bridge-1  | INFO[0000] backend/semtechudp: starting gateway udp listener  addr=""
bridge-lora-bridge-1  | ERRO[0000] [client]   dial tcp connect: connection refused  module=mqtt
bridge-lora-bridge-1  | WARN[0000] [client]   failed to connect to broker, trying next  module=mqtt
bridge-lora-bridge-1  | ERRO[0000] [client]   Failed to connect to a broker      module=mqtt
bridge-lora-bridge-1  | FATA[0000] network Error : dial tcp connect: connection refused
bridge-lora-bridge-1 exited with code 1

Contents to docker-composer.yml

version: "3.6"
    image: chirpstack/chirpstack-gateway-bridge
    stdin_open: true # docker run -i
    tty: true  # docker run -t
    privileged: true
      - C:\BRIDGE\.config:/etc/chirpstack-gateway-bridge/
      - 1883:1883
      - 1700:1700

Please search forums for this error, which likely has to do with docker not chirpstack.