I don’t know how cups-lpd needs to be configured with the ports, but for port 515 you can try creating a local firewall rule for the printer service (take care when opening ports to RED interface):
You may need to remove the service you created earlier:
config show printer
config delete printer
But if cups-lpd service needs to be associated with a port, you can recreate the service with the proper service name (I guess either printer or cups-lpd) and enable/activate the service (if it is a systemd service, if it uses xinetd or init the service might not show up on the server-manager).