CORE_VM_DOCKER_HOSTCONFIG_NETWORKMODE is set to "byfn_default" but this network interface does not exist, resulting in an error when trying to instanciate chainecode. As the docker compose file is in the folder "first-network", docker will create a default network called "firstnetwork_default", so should change the env. variable accordingly.
Other solution could be to define a custom network "byfn_default" in the docker-compose-cli.yaml file using top-level key "networks" (https://docs.docker.com/compose/networking/)
